UC-NRLF 


C    2 


Binary  Fission  in  Gollodictyon  triciliatum  Carter 


Robert  Clinton  Rhodes 

A  thesis  presented  to  the  Faculty  of  the 
College  of  Letters  and  Science 

in  the 

University  of  California 

In  partial  fulfillment  of  the  requirements 

for  the  degree  of 
Doctof  of  Philosophy. 


Approved  by  subcommittee  in  charge: 


Chairman, 

•  o 

Berkeley,  California. 


Cx  • 


BINARY  FISSION  IN  COLLODICTYON 
TRICILIATUM  CARTER 


A  THESIS  ACCEPTED  IN  PAETIAL  SATISFACTION  OF 
THE   REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 
AT  THE  UNIVERSITY  OF  CALIFORNIA 


ROBERT  CLINTON  RHODES 


1917 


Vol.  19,  No.  6,  pp.  201-274,  plates  7- 14,  4  figures  in  text.         December  3,  1919 


BINARY   FISSION   IN   COLLODICTYON 
TRICILIATUM   CARTER 


BY 
ROBERT   CLINTON    RHODES 


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BERKELEY 


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IN 

ZOOLOGY 

Vol.  19,  No.  6,  pp.  20 1-274,  plates  7- 14,  4  figures  in  text.         December  3,  1919 


BINARY  FISSION  IN  COLLODICTYON 
TRICILIATUM  CARTER 


BY 

EGBERT  CLINTON  EHODES 


CONTENTS 

PAGE 

Introductory  and  historical  201 

Material  and  technique 204 

General  morphology  209 

Habits  and  activities  219 

Mitosis 221 

Resting  stage 221 

Unequal  constriction  of  the  karyosome 223 

Mitosis 224 

Prophase  226 

Metaphase 229 

Anaphase  and  telophase  231 

Summary  of  observations 232 

Discussion 234 

Classification  and  relationships 234 

Parasitism  and  symbiosis  239 

Mitosis    : 241 

Kinetic  membrane  250 

Inheritance  in  binary  fission  252 

General  Summary 254 

Literature  cited 255 

Explanation  of  plates  260 


INTRODUCTORY  AND  HISTORICAL 

In  February,  1916,  I  found  in  an  aquarium  containing  goldfish 
a  dominant  and  persistent,  free  living  flagellate  which  seemed  to 
warrant  further  investigation.  Being  large  and  transparent,  except 
when  filled  with  green  and  opaque  inclusions,  and  occurring  in  quan- 
tities, it  presented  an  opportunity  for  continuous  and  repeated 


431559 


'*'*  1*1  ^'.-"^  V"1  .,.* 

202  University  of  California  Publications  in  Zoology        [VOL.  19 

observations,  especially  upon  its  metabolic  character  and  nuclear 
changes.  The  form  has  been  identified  as  Collodictyon  triciliatum 
Carter  (=Tetramitus  sulcatus  Stein). 

This  genus  was  first  described  by  Carter  (1865,  p.  289)  as  follows: 

Collodictyon,  nov.  gen.  C.  triciliatum,  nov.  sp. 

Pyriform,  straight,  or  slightly  bent  upon  itself,  bifid  at  the  small  extremity, 
presenting  at  the  larger  one  an  indentation,  from  which  spring  three  cilia. 
Structure  transparent,  cancellated,  composed  of  globular  cells,  with  a  strongly 
marked,  greenish  granule  here  and  there  in  the  triangular  spaces  between  them. 
Locomotive,  swimming  by  means  of  the  cilia;  subpolymorphic,  flexible,  yielding, 
capable  of  assuming  a  globular  form  ...  or  one  more  or  less  modified  by  the 
body  it  may  incept  .  .  .  ;  enclosing  crude  material  for  nourishment  in  stomachal 
spaces,  and  ejecting  the  refuse,  like  Amoeba.  Provided  with  a  nucleus  and 
contracting  vesicles. 

He  gave  its  habitat  (p.  289)  as  "fresh  water,  chiefly  among  Euglena 
and  Infusoria  of  that  kind."  Its  length  was  1/771  in.  (30/i)  and  its 
location  the  Island  of  Bombay.  Among  his  observations  he  added 
(p.  289)  the  following:  "The  plastic  nature  of  this  Infusorium,  and 
its  mode  of  incepting  food  being  like  that  of  Amoeba  (for  it  does  not 
appear  to  possess  any  oral  aperture),  induce  me  to  think  that  it  should 
be  placed  among  the  Rhizopoda.  Still  it  seems  to  have  some  analogies 
to  Bodo  Ehr."  "Its  generic  name  has  been  derived  from  its  plasticity 
and  delicate  cellular  structure,  which  gives  it  a  reticular  or  cancellated 
appearance;  and  its  specific  designation  from  the  presence  of  three 
cilia." 

The  above  description  is  satisfactory  for  identification,  though  not 
detailed.  My  own  observations  coincide  with  it  with  these  exceptions : 
there  are  four  instead  of  three  flagella;  it  may  or  may  not  be  bifid 
at  the  posterior  end ;  there  is  at  the  anterior  end  of  the  body  a 
blepharoplast  from  which  the  flagella  arise,  these  not  springing  from, 
but  near  the  indentation,  which  is  a  continuation  of  the  median  groove, 
or  sulcus,  which  functions  in  food  ingestion;  I  have  found  no  con- 
tracting vacuole,  though  Carter  stated  that  he  had  observed  ' '  contract- 
ing vesicles"  having  no  fixed  position,  but  he  figures  none. 

In  1878  Stein  figured  a  similar  form,  showing,  however,  the  four 
flagella,  a  median  sulcus  and  a  contractile  vacuole,  naming  it  Tetra- 
mitus  sulcatus.  Kent  (1880-1882,  p.  314)  accepted  these  organisms 
as  described  by  Carter  and  Stein  as  belonging  to  separate  genera  of 
the  family  Trimastigidae,  but  that  there  is  little  cause  for  such  a 
distinction  can  be  seen  from  his  characterization  of  Stein's  genus  as 
follows : 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    203 

Body  obtusely  pyriform  or  subcordate,  widest  and  rounded  anteriorly,  taper- 
ing towards  and  bluntly  pointed  at  the  posterior  extremity,  about  one  and  a 
half  times  as  long  as  broad;  a  deep  groove  traversing  the  entire  length  of  the 
centre  of  the  ventral  side  and  imparting  to  the  posterior  extremity,  as  seen 
from  beneath,  a  bilobate  contour;  flagella  four  in  number,  of  equal  length, 
inserted  close  together  in  the  centre  of  the  anterior  border;  endoplast  and 
contractile  vesicle  located  side  by  side  near  the  same  anterior  margin;  par- 
enchyma granular,  soft  and  plastic.  Length  1/700.  Hab.,  fresh  water. 

Biitschli  (1887,  p.  841)  recognized  these  two  forms  as  the  same 
and  Tetramitus  sulcatus  Stein  as  a  synonym  of  Collodictyon  triciliatum 
Carter,  characterizing  the  genus  as  follows  under  the  family  Tetra- 
mitina : 

Massig  gross  (L.  bis  0,035  Mm.),  estalt  vorn  etwas  verbreitert  und  quer 
abgestutzt,  nach  hinten  wenig  verschmalert  und  abgerundet.  Wahrscheinlich 
etwas  abgeplattet;  iiber  die  eine  Flache  zieht  eine  breite  Langsfurche  hinab. 
Vorderende  mit  vier  gleich  langen  aus  einem  Punkt  entspringenden  Geisseln 
(Carter  gibt  nur  drei  an).  Nucleus  und  contractile  vacuole  im  Vorderende. 
Nahrungsaufname  sicher.  Vermehrung  durch  Langstheilung.  Siisswasser. 
Europa  und  Ostindien. 

In  1893  Klebs  investigated  a  form  which  he  designated  as  Tetra- 
mitus sulcatus  Stein.  He  found  the  four  flagella  of  unequal  length 
and  a  contractile  vacuole  in  the  posterior  end  of  the  body,  the  longi- 
tudinal furrow  a  spiral,  the  size  being  17  by  15  microns.  These  differ- 
ences lead  me  to  conclude,  after  careful  consideration  of  his  descrip- 
tion and  figures,  that  he  is  mistaken  in  his  verification  and  the  form 
he  described  is  not  Collodictyon  triciliatum,  but  probably  some  species 
of  Tetramitus. 

France  (1899)  studied  Carter's  organism  thoroughly;  his  descrip- 
tion is  accurate  and  detailed,  his  figures  typical  and  true  to  life.  My 
own  observations  coincide  with  his  in  practically  all  details.  He  con- 
cluded that  Klebs'  (1893)  description  was  not  of  Collodictyon.  He 
dealt  fully  with  the  morphological  features  and  metabolic  changes,  to 
which  I  have  little  to  add.  In  only  one  important  point  do  our 
observations  fail  to  agree.  I  can  find  no  contracting  vacuole.  He  left 
untouched,  however,  the  method  of  mitosis,  merely  stating  that  repro- 
duction was  by  longitudinal  division,  which  was  also  noted  by  Carter 
(1865)  ;  it  is  to  this  especially  that  I  shall  address  myself. 

I  am  indebted  to  Dr.  Olive  Swezy  for  suggesting  the  desirability 
of  working  out  the  mitosis  of  this  form,  the  correction  of  the  bibli- 
ography, sketching  figures  75,  78,  and  83  of  plate  8,  in  my  absence, 
and  for  repeated  criticism  and  help.  I  also  wish  to  thank  Professor 


204  University  of  California  Publications  in  Zoology        [VOL.  19 

C.  A.  Kofoid  for  his  suggestive  interpretations  and  criticisms,  both 
constructive  and  destructive,  and  for  the  determination  of  the  extra- 
nuclear  division  center. 


MATERIAL  AND  TECHNIQUE 

Plentiful  material  was  found  in  an  aquarium  where  goldfish 
were  kept.  These  were  obtained  from  the  Yorizuya  Company,  who 
represent  the  Nippon  Gold  Fish  Company  and  import  direct  from 
Japan.  In  no  other  cultures  have  I  found  Collodictyon.  Since  it  has 
only  been  noted  from  India  and  central  Europe,  it  is  possible  that  it 
is  not  native  to  California,  and  may  have  been  introduced  with  the 
importation  of  goldfish  from  Asia  or  Hawaii.  On  the  voyage  from 
Japan,  however,  the  barrels  in  which  the  fish  are  contained  are 
emptied  and  fresh  water  added  at  Hawaii  and  also  at  the  wharf  in 
San  Francisco.  It  would  be  easy  for  the  flagellates  to  be  brought 
through  notwithstanding  this  change  of  water,  either  by  being  trans- 
ferred with  the  fish,  with  water  plants  which  are  brought  in  the  same 
aquaria,  or  by  clinging  to  the  moist  sides  of  the  containers  (barrels). 
Thus,  though  there  is  a  possibility  that  Collodictyon  has  been  intro- 
duced into  California,  the  cosmopolitan  distribution  of  Protozoa  makes 
this  highly  improbable,  and  this  genus  may  be  regarded  as  indigenous. 

These  forms  have  persisted  and  usually  have  been  dominant  in  an 
aquarium  26.5  x  60  x  20  cm.,  the  bottom  of  which  is  covered  with  sand 
to  a  depth  of  about  an  inch,  in  which  Ulothrix  has  grown  in  quantities 
and  to  which  I  have  added  Lemna,  Ranunculus,  and  Myriophyllum. 
At  least  one  goldfish  has  been  present  all  the  time,  at  times  two  and 
four.  These  fish  have  fed  freely  on  the  plant  life  of  the  aquarium, 
making  it  necessary  to  replenish  all  higher  plants  and  on  more  than 
one  occasion,  the  algae,  although  the  aquarium  has  been  sufficiently 
well  balanced  for  one  fish  to  survive  since  January,  1916.  The  aqua- 
rium has  been  placed  outside  a  window  with  southern  exposure,  partly 
protected  by  glass  plate  and  wooden  cover.  The  variations  of  tem- 
perature for  the  year  have  been  from  about  28°  F  to  92°  F.  Con- 
siderable variation  of  temperature  from  the  heat  of  the  direct  rays  of 
the  sun  at  mid-day  to  the  cool  nights  failed  to  destroy  the  culture. 
Since  the  cooler  weather  of  last  December  Collodictyon  has  been  sup- 
planted at  intervals  by  a  dinoflagellate,  Peridinium  penardii  Lemm., 
as  the  dominant  organism,  the  latter  seeming  to  be  favored  by  the 
cooler  weather.  On  one  occasion  the  aquarium  froze  over  during  the 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    205 

night,  the  ice  being  one-eighth  to  one-quarter  of  an  inch  in  thickness, 
forming  at  a  temperature  of  28°  F.  Under  the  ice  and  throughout 
the  following  day  Collodictyon  seemed  even  more  numerous  than  ever 
and  many  dividing  forms  were  found.  The  following  night,  tempera- 
ture 32°  F,  abundant  mitotic  stages  of  Collodictyon  and  Peridinium 
were  found.  Many  of  the  dinoflagellates  escaped  from  their  theca  by 
ecdysis  and  many  division  stages  were  observed.  Greeley  (1903) 
noted  the  effect  of  reduction  of  temperature  upon  the  artificial  pro- 
duction of  spore  formation  and  multiple  fission  in  Monas.  I  obtained 
nothing  resembling  resting  spores  or  somatellas.  At  4°  C  Greeley 
(1903)  found  that  Monas  rounded  up  into  a  resting  spore  in  about 
six  hours,  and  at  1°  C  multiple  fission,  resulting  in  a  resting  somatella, 
was  observed  within  five  days.  It  is  interesting  to  note  in  comparison 
that  binary  fission  was  simply  accelerated  in  both  Collodictyon  and 
Peridinium  at  a  temperature  of  32°  and  28°  F. 

Collodictyon  seemed  most  abundant  on  the  surface,  naturally  tend- 
ing to  accumulate  in  the  corners  and  around  the  edges  of  the  aqua- 
rium. But  during  the  day  and  night  at  all  temperatures  above  freez- 
ing, I  have  found  them  present  throughout  the  aquarium,  from  the 
bottom  to  the  top,  under  the  protected  area  as  well  as  the  open  end. 
I  placed  slides  and  covers,  suspended  at  various  depths,  as  well  as 
covers  suspended  in  cylinders  to  eliminate  currents,  and  found 
abundant  organisms  in  all  parts  of  the  aquarium.  In  these  experi- 
ments, attempted  primarily  to  determine  the  time  and  conditions  of 
division  and  probable  multiple  fission,  I  was  led  to  conclude  that 
division  was  determined  more  by  chemical  than  physical  conditions, 
that  it  was  no  more  abundant  at  night  than  during  the  day,  that 
individuals  undergoing  binary  fission  remained  at  the  surface  for  the 
most  part,  but  could  be  found  at  all  depths,  in  all  degrees  of  light  and 
temperature,  though  more  abundant  at  32°  F.  At  no  time  have  I 
found  a  clear  case  of  multiple  fission.  One  instance  (pi.  7,  fig.  62) 
of  a  somatella  was  observed,  but  on  careful  comparison  of  the  stain- 
ing reactions,  I  was  led  to  conclude  that  this  was  a  cyst  of  Amoeba 
radiosa,  vegetative  stages  of  which  were  abundant  in  the  aquarium. 
The  life  cycle  of  Collodictyon,  as  far  as  traced,  is  thus  simple,  repro- 
duction being  by  binary  fission  only.  "When  the  organisms  wholly 
disappear  from  the  cultures,  I  have  been  unable,  by  varying  con- 
ditions, to  start  the  culture  up  again.  It  seems,  therefore,  that  there 
may  be  no  cysts  or  resting  stages  for  this  flagellate,  at  least  under 
the  conditions  observed.  The  extreme  variations  in  size  (pi.  2,  figs. 


206  University  of  California  Publications  in  Zoology        [Voi .  19 

5-6)  would  naturally  lead  one  to  suspect  a  somatella  stage,  though  this 
variation  may  be  accomplished  by  reduction  through  successive  binary 
fissions. 

In  culture  experiments  I  have  tried  malted  milk  (one-sixteenth  of 
one  per  cent  solution  and  varying  strengths),  crushed  Myriophyllum, 
boiled  mushroom  solution,  amoeba  agar,  sterilized  soil  with  tap  water 
boiled  thirty-five  minutes,  beef  extracts,  and  quince-seed  jelly  as  sug- 
gested by  Turner  (1917)  for  Euglena.  Most  of  these  were  partially 
successful,  but  only  temporarily  so,  Collodictyon  soon  disappearing 
from  the  culture. 

Among  associated  forms  in  the  aquarium,  I  have  found :  Pandorina, 
Peridinium,  Euglena,  Amoeba  of  the  Umax  group  and  others,  Platy- 
dorina,  Gonium,  Actinoplirys,  Bodo,  Chlamydomonas,  Chilomonas, 
Coleps,  Stylonychia,  Euplotes  patella  and  E.  charon,  Microthorax,  and 
Colpidium;  rotifers  (Branchionus,  Philodina,  and  Chaetonotus}  ; 
Ulothrix,  Oscillatoria,  Chlorella,  Tetraspora,  Spongomonas,  Lager- 
heimia,  Scenedesmus,  Pediastrum,  Selenastrum,  Coleochaete,  Navicula, 
Closterium,  Cosmarium,  and  several  undetermined  desmids  and 
diatoms. 

I  have  considered  the  possibility  that  the  life  history  of  Collodictyon 
may  in  some  way  be  related  to  its  association  with  goldfish.  Aside 
from  the  balancing  of  the  plant  and  animal  life  of  the  aquarium,  I 
have  looked  for  some  symbiotic  or  parasitic  relationship,  but  have 
found  none,  other  than  the  fact  that  I  have  been  unable  to  keep  a 
permanent  culture  in  other  than  a  goldfish  aquarium.  I  tried  a  fairly 
well  balanced  stickleback  aquarium  without  success.  In  aquaria  where 
there  were  abundant  Ulothrix  and  other  algae,  Collodictyon  did  not 
persist.  The  voracious  habits  of  this  animal  led  me  to  believe  that  it 
is  not  symbiotically  dependent  upon  goldfish,  nor  has  it  any  other 
method  of  food-taking  involving  absorption;  but  its  habits  of  engulf- 
ing free  living  protozoa  and  algae  may  wed  it  to  a  well  balanced  con- 
dition such  as  would  be  found  in  a  satisfactory  goldfish  aquarium. 
There  is  a  bare  possibility  that  the  life-history  is  dependent  upon  the 
presence  of  living  fish,  though  Carter  and  France's  observations  are 
opposed  to  such  an  interpretation.  In  examination  of  stomach  and 
intestinal  contents  I  found  no  evidence  of  symbiosis  or  parasitism 
relating  the  two.  Examination  of  the  gills  and  body  for  ectoparasites 
never  failed  to  yield  some  of  these  forms.  This  was  probably  due, 
however,  to  their  abundance  in  the  water. 

It  is  rather  a  prevalent  custom  to  use  cover-glass  preparations  in 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    207 

protozoan  technique.  I  refer  here  not  to  Romano wsky 's  dry  film, 
which  has  no  general  use  or  approval,  but  to  a  modification  of  Schau- 
dinn's  moist  film  method,  which  involves  the  use  of  some  fixative, 
pipetting  the  organisms  on  to  the  cover  smeared  with  this  and  then 
the  evaporation  of  the  water  until  the  animals  will  adhere  to  the 
cover  when  dropped  or  floated  directly  on  the  surface  of  the  killing 
fluid.  I  found  on  attempting  this  method  that  conditions  accompany- 
ing the  evaporation  process  ruptured  the  body,  and  normal  killing  or 
fixation  could  not  be  obtained  with  Collodictyon,  which  is  evidently 
more  susceptible  than  many  other  free  living  forms. 

Collodictyon  when  exposed  to  excessive  evaporation  may  rupture 
instantaneously  or  more  frequently  pass  through  moribund  phases  as 
shown  in  text  figure  C.  All  foreign  bodies  are  ejected,  the  vacuoles 
become  larger,  gradually  fuse  into  still  larger  pathological  vacuoles, 
which  finally  rupture.  The  organism  becomes  much  distorted  and 
disintegration  usually  takes  place  along  the  sulcus. 

Wherever  the  death  rate  is  above  the  normal  or  even  at  equilibrium, 
the  number  of  abnormal  moribund  forms  is  undoubtedly  great.  Many 
life  cycles  could  be  and  possibly  have  been  built  up  on  such  fallacious 
interpretations.  Protozoa  may  be  potentially  immortal  but  the  vast 
majority  do  not  survive.  The  real  problem,  therefore,  is  to  find  some 
way  to  determine  the  normal  from  the  moribund,  either  physiologically 
or  pathologically  abnormal. 

I  resorted  to  killing  en  masse,  either  with  or  without  centrifuging. 
I  found  that  in  lightly  centrifuged  material  there  was  no  nuclear  dis- 
placement or  other  variations  which  could  be  detected  from  the  non- 
centrifuged,  so  I  adopted  the  centrifuge  as  the  best  and  quickest 
method  of  running  up  the  material.  After  a  normal  killing  in  a  beaker 
and  running  up  through  the  alcohols  in  centrifuge  tubes,  some  of  the 
organisms  were  then  fixed  to  covers,  where  it  was  essential  for  the 
quick  handling  of  material,  as  in  Mallory  's  stain.  I  also  found  it 
convenient  and  satisfactory  in  dehydrating  rapidly  after  certain  stains, 
as  in  phosphotungstic  haematoxylin,  to  pass  from  an  aqueous  stain 
by  adding  3  to  5  c.c.  of  50  per  cent  and  then  40  to  50  c.c.  of  absolute 
alcohol,  immediately  centrifuging  and  adding  carboxylol. 

At  times  Collodictyon  was  found  to  be  rapidly  increasing  in  num- 
bers in  the  aquarium  and  from  this  it  was  judged  that  there  was  little 
or  no  death  taking  place,  but  that  conditions  were  favorable  for  a 
maximum  growth  and  normal  reproduction.  Material  collected  at 
such  times  as  this  was  regarded  as  normal,  at  least  for  the  phase  of 


208  University  of  California  Publications  in  Zoology        [VOL.  19 

purely  vegetative  existence.  By  collecting  water  from  the  aquarium 
and  putting  in  petri  dishes  I  was  at  times  able  to  get  a  determinate 
increase  in  numbers  and  low  mortality.  By  killing  at  such  times, 
material  normal  as  it  was  possible  to  get  was  obtained.  Various 
methods  of  introducing  the  material  to  the  killing  fluid  was  used :  by 
pipette,  by  pouring,  or  by  pouring  the  killing  fluid  on  concentrated 
masses  of  the  organisms.  The  proportion  of  the  killing  fluid  was  never 
allowed  to  be  less  than  ten  times  the  amount  of  the  water  containing 
the  flagellates. 

The  most  satisfactory  material  was  obtained  by  killing  either  in  hot 
Schaudinn's  fluid  or  strong  Flemming,  and  staining  in  Heidenhain's 
aqueous  iron  haematoxylin.  By  this  method  the  nuclear  differentiation 
becomes  evident  as  figured  in  accompanying  plates.  Counterstaining 
in  eosin,  either  just  after  destaining  or  from  50  per  cent  alcohol,  brings 
out  the  flagella. 

Other  killing  fluids  used  in  addition  to  Schaudinn's  and  strong 
Flemming  were:  picro-mercuric,  Gilson's,  Flemming 's  weak,  Carnoy's, 
Zenker's,  Bouin's,  and  osmic  acid.  None  of  these  was  perfectly  satis- 
factory, possibly  through  lack  of  proper  proportions  or  some  un- 
detected flaw  in  technique. 

Heidenhain's  aqueous  iron  alum  haematoxylin  I  regard  as  by  far 
the  safest,  most  differential  and  permanent  stain.  Alcoholic  solutions 
were  about  as  satisfactory,  but  required  from  one  to  two  hours  for  the 
mordant  and  eight  to  twenty-four  for  the  stain,  thus  not  being  much 
quicker  than  the  aqueous  solutions.  Acid  fuchsin  or  eosin  were 
excellent  counterstains  with  either  of  the  above.  Delafield's  haema- 
toxylin yielded  beautiful  but  not  so  critical  a  differentiation.  The 
granular  organization  of  the  chromatin,  even  of  the  karyosome,  was 
emphasized.  Phosphotungstic  acid  haematoxylin  was  of  assistance  in 
determining  the  nuclear  membrane,  but  did  not  show  up  the  spindle 
fibers  as  was  hoped.  Mallory's  connective  tissue  stain  as  modified  for 
Protozoa  yielded  only  fairly  satisfactory  results  with  the  fixatives 
tried.  By  its  use  the  two  basal  granules  embedded  in  the  blepharoplast 
could  be  distinguished.  For  some  reason  Collodictyon  seems  able  to 
withstand  chemicals,  especially  the  usually  quick  stains,  far  more  than 
other  free  living  Protozoa  with  which  I  have  dealt,  the  time  required 
for  all  stains  being  longer  than  that  ordinarily  scheduled.  Flemming 's 
safranin,  gentian-violet,  orange  G  was  tried,  for  the  purpose  of  differ- 
entiating the  macrokaryosomes  and  microkaryosomes,  but  no  variations 
of  color  diagnostic  of  chemical  differences  were  obtained.  The 


Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    209 

cytoplasmic  differentiation,  however,  was  good.  The  blepharoplast  and 
evidence  of  a  rhizoplast  were  emphasized  by  preceding  Heidenhain's 
iron  haematoxylin  with  weak  Bordeaux  red  for  twenty-four  to  thirty- 
six  hours,  and  destaining  until  the  chromatin  was  almost  colorless,  as 
directed  by  Heidenhain.  Paracarmine  with  aluminum  chloride  as 
mordant  did  not  yield  satisfactory  results.  Collodictyon  proved  sus- 
ceptible to  neutral  red  and  methylen  blue  of  the  intra-vitam  stains. 
It  was  unaffected  by  Bismarck  brown.  Neutral  red  after  a  consider- 
able time  differentiated  the  food  vacuoles  and  acted  somewhat  upon 
the  plasma.  It  never  disclosed  a  pulsating  vacuole.  Methylen  blue 
largely  reacted  upon  the  plasma  and  was  not  differential,  possibly 
showing  up  the  protoplasmic  vacuoles  with  some  intensity. 

In  order  to  section  I  resorted  to  the  capsule  method  of  embedding. 
The  material  was  taken  from  the  xylol-paraffine,  saturated  solution, 
in  the  centrifuge  tube,  and  placed  in  a  capsule.  Melted  paraffine  was 
dropped  in  and  this  process  was  repeated  successively  until  the  material 
was  satisfactorily  embedded.  Sections  were  cut  3,  5,  and  7//,  thick. 


GENERAL  MORPHOLOGY 

Collodictyon  is  variable  both  in  size  and  shape.  Its  length  is  15 
to  60/i ;  width,  10  to  40//, ;  thickness,  8  to  36/x.  These  figures  show  that 
many  of  the  individuals  I  have  found  are  smaller  than  those  recog- 
nized by  previous  observers.  The  typical  shape  of  the  body  (pi.  7, 
figs.  1-4)  is  ovoid,  cordate  or  bifurcated  posteriorly.  A  longitudinal 
furrow,  or  sulcus,  is  always  present,  though  at  times  showing  only  a 
slight  indentation,  but  usually  evident  as  a  deep  groove  on  one  of  the 
narrower  sides.  Four  equal  flagella  about  as  long  as  the  organism 
arise  from  the  anterior  ovoid  end.  Anteriorly  the  body  is  ovoid,  at 
times  cordate,  the  sulcus  extending  around  as  an  indentation.  The 
general  shape  is  rounded  or  compressed  in  the  plane  running  through 
the  sulcus,  the  nucleus  and  the  blepharoplast.  The  posterior  end  may 
be  truncated,  oval,  acuminate,  bifid,  with  the  cusps  pointing  posteriorly, 
curved  spirally  or  diverging  at  an  angle  up  to  seventy-five  degrees,  or 
with  three,  four,  or  five  cusps  (pi.  7,  figs.  5-8)  caused  by  secondary 
sulci  which  run  parallel  to  the  primary  longitudinal  sulcus.  Changes 
of  form  are  gradual  except  when  altered  by  engulfed  food  or  the 
extrusion  of  undigested  products.  The  peculiarities  of  the  posterior 
cusps  are  held  by  a  single  individual  indefinitely.  Few  individuals, 
if  any,  are  exactly  alike  in  form. 


210 


University  of  California  Publications  in  Zoology        [VOL.  19 


Seldom  does  the  sulcus  extend  far  enough  forward  to  modify  the 
regularity  of  the  anterior  end,  which  is  fairly  constant  in  form,  much 
more  so  than  the  posterior  end.  This  sulcus  is  a  furrow  or  depression 
which  cleaves  the  body  on  one  side,  which  side  may  consistently  be 
called  sulcal  or  adsulcal,  analogous  to  ventral,  as  opposed  to  absulcal, 
which  is  analogous  to  dorsal.  The  secondary  sulci  usually  branch 
from  the  chief  longitudinal  sulcus,  the  resulting  cusps  being  variable 
in  size,  shape  and  permanence.  At  times  the  general  form  becomes 
spherical  and  globular,  the  posterior  end  truncated,  or  ovate  and 
conical,  with  acute  posterior  end,  the  sulcus  being  faint  in  both  cases. 


Fig.  A.  Pseudopodia  of  Collodictyon.  Diagrammatic.  X  1000.  1-2.  Lobose. 
3.  Undulate.  4.  Digitate.  5.  Filose.  1-5.  From  the  sulcus.  6.  From  all  parts  of 
the  surface. 

The  four  flagella  are  paired,  each  pair  arising  from  a  single  basal 
granule,  the  two  granules  being  embedded  in  the  irregular  chromatoidal 
blepharoplast  which  is  surrounded  by  a  granular,  less  darkly  staining 
archoplasm  or  modified  cytoplasm.  The  flagella  are  typically  whip- 
like,  in  length  averaging  that  of  the  major  axis  of  the  body,  at  times 
a  little  longer,  measuring  in  one  instance  68  to  TOyu,.  They  taper 
toward  the  tip.  France  (1899)  used  zinc  chloride  to  bring  out  their 
full  length  and  further  observed  their  base  to  be  granular.  Language 
is  inadequate  to  describe  the  beauty  of  their  elegant  backward  curves. 
They  function  both  in  pulling  and  propelling  the  body  forward,  in 
attachment  to  the  substrate  while  the  organism  rotates  on  its  major 
axis,  as  a  tactile  organ  for  directing  locomotion,  and  actively  in  offense 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    211 

and  defense.  In  attacking  a  dinoflagellate  they  were  observed  to  catch 
their  prey  with  all  four  flagella;  they  then  allowed  themselves  to  be 
pulled  about  until  the  dinoflagellate  was  exhausted,  when  it  was  drawn 
back  to  the  anterior  end  of  the  sulcus  and  engulfed.  On  another 
occasion  when  Collodictyon  was  being  drawn  toward  the  mouth  of  a 
rotifer,  it  spread  its  flagella  and  lodged  upon  the  oral  membrane;  at 
other  times  it  was  enabled  to  guide  itself  to  one  side  of  the  oral  current. 
While  not  the  most  conspicuous,  the  flagella  constitute  the  most  useful 
organelles  of  this  slightly  differentiated  unicellular  organism. 


Fig.  B.  1-4.  Extrusion  of  Lagerheimia  by  Collodictyon,  showing  false  pseudo- 
podia.  5-8.  Unsuccessful  attempt  of  Collodictyon  to  engulf  long  Ulothrix  fila- 
ment. Diagrammatic.  X  750.  5.  Extension  of  protoplasmic  sheath  along 
filament.  6.  Contraction  of  protoplasmic  sheath  forcing  the  filament  anteriorly, 
pushing  out  the  surface.  This  was  repeated  several  times.  7.  Retraction  of 
protoplasmic  sheath.  8.  Extrusion  of  filament. 

The  sulcus  is  usually  a  smooth  depression,  but  when  Collodictyon 
is  actively  searching  for  food,  pseudopodia  are  extended  from  any  or 
all  portions  of  the  sulcal  region.  These  may  be  of  various  types, 
hatchet-shaped,  lobose,  finger-like,  or  filose  (text  fig.  A,  1-5).  Finger- 
like  pseudopodia  from  over  the  entire  surface  of  the  body  were  observed 
(text  fig.  A,  6),  but  such  are  very  rare.  The  entire  sulcus  at  times 
may  become  serrated  and  undulating,  exceedingly  amoeboid  and  meta- 
bolic. The  posterior  end  may  put  forth  lobose  pseudopodia  or  flow 
around  objects  being  engulfed  (text  fig.  B,  1-6).  The  posterior  cusps 


212  University  of  California  Publications  in  Zoology        [VOL.  19 

are  themselves  slightly  amoeboid  and  may  slowly  change  position  and 
form,  though  this  is  unusual. 

On  many  occasions  I  have  noticed  a  change  of  form  of  a  different 
character  and  at  first  thought  true  pseudopodia  were  being  extended 
from  the  whole  body  surface,  but  by  continued  observations  it  was 
discovered  that  some  undigested  plant,  as  Scenedesmus  or  Lagerheimia, 
was  escaping  or  being  extruded  (text  fig.  B,  1-4).  The  pellicle  and 
cytoplasm  extended  out  around  the  rays  or  processes  and  undoubtedly 
part  of  the  cytoplasm  was  lost  when  the  object  was  set  free.  The 
cytoplasm  immediately  contracted,  the  ruptured  edges  or  margins  drew 
closer  together  until  they  were  rounded  up  and  fused  (text  fig.  C,  1-7). 
This  seemed  not  so  much  a  healing  process  as  simply  protoplasmic 
contraction  and  rounding  up.  I  have  noticed  on  two  occasions,  how- 
ever, that  the  ruptured  edges  met  and  fused,  enclosing  a  water  vacuole 
in  the  healing  or  coalescing  process  (text  fig.  C,  5).  These  phenomena 
make  it  evident  that  there  is  no  cuticle  and  that  the  pellicle  has 
developed  little  beyond  the  state  of  a  firm  protoplasmic  gel.  Changes 
in  shape  in  the  sulcal  region  are  amoeboid,  most  other  changes  involv- 
ing the  whole  body  are  metabolic  or  euglenoid.  There  is  no  differ- 
entiation of  ectoplasm  and  endoplasm.  The  surface  is  exceptionally 
smooth  and  well  rounded,  in  spite  of  the  fact  that  the  cytoplasm  is 
highly  vacuolated. 

The  function  of  the  sulcal  region  is  not  hard  to  determine,  for  un- 
doubtedly it  is  through  this  region  almost  altogether  that  food  is 
ingested ;  but  to  decide  its  true  status  and  homology  is  a  more  difficult 
problem.  It  is  a  restricted  area  of  the  body,  which  has  either  retained 
or  evolved  an  amoeboid  and  miscible  surface.  It  is  always  a  unit, 
a  persistent  though  variable  character,  and  of  constant  function. 
Amoeboid  pseudopodia  are  almost  entirely  restricted  to  this  area. 
Many  flagellates,  such  as  Euglena  and  Astasia,  are  exceedingly  meta- 
bolic, constantly  varying  in  shape,  but  they  have  no  such  differentiated 
surface  area  as  this  found  in  Collodictyon.  Mastigamoeba  is  classified 
as  a  polarized  rhizopod,  the  entire  surface  of  which  is  amoeboid.  The 
exceeding  voraciousness  of  Collodictyon  is  indicative  of  a  fairly  ad- 
vanced organism  and  in  view  of  this  fact  it  seems  best  to  regard  the 
whole  sulcal  region  as  a  modified  cytostome.  It  must  be  considered 
more  homologous  to  the  amoeboid  surface  of  Mastigamoeba,  however, 
than  to  the  more  restricted  gullet  of  Euglena,  which  is  probably 
homologous  with  only  the  anterior  end  of  the  sulcus.  This  structure 
indicates  a  possible  origin  of  the  more  specialized  cytostomes  as  found 


1919]     Rhodes :  Binary  Fission  in  Collodictyon  triciliatum  Carter    213 

in  Trichomonas,  Costia,  and  Giardia.  Collodictyon  must  in  any  case 
be  looked  upon  as  a  form  of  simpler  organization  and  probably  of  a 
more  primitive  type  than  these  parasitic  forms. 

The  anterior  extremity  of  the  sulcus,  just  beside  the  base  of  the 
flagella,  may  be  modified  into  a  depression  (pi.  9,  fig.  19)  which  has 


Fig.  C.  Escape  of  Pandorina  and  subsequent  dissolution  of  Collodictyon  due 
to  drying.  Diagrammatic.  X  750.  1.  Pandorina  within  food  vacuole.  2.  Pan- 
dorina swimming  away;  ruptured  surface  of  Collodictyon.  3,  4.  Apparent  healing 
of  torn  surface.  5.  Fusion  of  ends  of  protoplasmic  processes,  enclosing  water 
vacuole;  of  frequent  occurrence.  6-8.  Eesorption  of  protoplasmic  processes. 
8,  9.  Flattening  of  body;  formation  of  pathological  vacuoles  indicative  of  dis- 
solution. 10.  Bursting  of  vacuole  at  anterior  region  of  sulcus.  11.  Further  dis- 
solution, rupturing  posteriad  along  the  sulcus.  12.  Nucleus  and  blepharoplast 
freed  by  dissolution,  a.  Nucleus;  nuclear  membrane  persisted  for  two  minutes. 
b.  Eupture  of  nuclear  membrane,  c.  Karyosome;  persisted  for  thirty  minutes; 
finally  broke  up  into  small  granules,  d.  Blepharoplast;  basal  granules  sur- 
rounded by  archoplasm,  flagella  still  moving,  e.  Kupturing  of  archoplasmic  mass; 
flagella  cease  beating. 

a  probable  function  of  a  more  specialized  cytostome.  It  takes  the  form 
of  a  permanent  depression  in  an  amoeboid  surface.  It  does  not  usually 
function  in  food  getting,  for  this  is  accomplished  by  the  amoeboid 
surface  of  the  entire  sulcal  region.  I  have,  however,  observed  uni- 
cellular algae  and  small  dinoflagellates  engulfed  through  or  near  this 


214  University  of  California  Publications  in  Zoology        [V<>L- 19 

depression.  Here  then  is  a  structure  which  by  location  and  analogy 
may  be  correlated,  or  at  least  compared,  with  the  highly  specialized 
gullet  of  forms  like  Euglena. 

There  is  a  tendency  at  times  for  Collodictyon  to  become  exceedingly 
eccentric  in  its  form  (pi.  8,  figs.  9-18).  Its  irregularity  is  for  the 
most  part  accompanied  by  a  flattening  and  warping,  the  sulcus  cleav- 
ing one  of  the  narrow  margins,  making  a  secondary  if  not,  indeed,  a 
fundamental  bilateral  symmetry.  On  occasions  when  such  irregu- 
larities were  prevalent,  I  have  tested  the  culture,  trying  to  determine 
if  possible  a  cause  for  such  variation.  The  water  of  the  aquarium  was 
neutral  or  only  slightly  alkaline,  by  litmus  paper  and  litmus  solution 
tests.  Alkalinity  tended  to  produce  rounded,  globular,  conical,  or  pear- 
shaped  forms,  the  sulcus  itself  being  reduced  to  a  minimum.  Con- 
centration tests  were  not  accurate,  but  in  my  judgment  I  could  detect 
no  variation  upon  this.  Death  always  resulted  when  the  density 
was  such  as  might  be  judged  sufficient  to  rupture  such  a  fragile 
organism.  That  oxygen  content  plays  an  important  part  in  the  vari- 
ation in  shape  there  can  be  no  doubt.  Sufficient  or  excessive  oxygen 
supply  tends  to  produce  well  rounded  forms,  a  deficient  supply,  flat- 
tened, eccentric  forms.  This  test  was  easily  made  by  having  a  sub- 
strate of  filamentous  and  unicellular  algae,  which  in  the  sunshine  kept 
the  aquarium  filled  with  bubbles  of  oxygen.  The  alternative  inter- 
pretation that  light  and  heat  caused  the  rounding  up,  was  tested  by 
placing  the  aquarium  without  any  algae  in  the  sunlight.  The  forms 
then  retained  their  original  shapes.  The  chemical  content  so  far  as 
organic  salts  in  solution  is  concerned  was  probably  not  variable  enough 
to  produce  the  variations,  tests  having  been  made  for  sodium,  calcium, 
and  magnesium  salts  with  negative  results.  By  adding  carbon  dioxide 
slowly  in  small  quantities  similar  eccentricities  of  shape  resulted  as 
from  deficient  oxygen.  From  these  tests  I  concluded  that  variation  of 
shape  was  largely  a  question  of  respiration,  irregularities  being  either 
degenerative  stages  or  adaptations  to  meet  deficient  oxygen  supply. 
Carbon  dioxide  in  excessive  amounts  would  be  immediately  converted 
into  carbonic  acid  gas  and  thus  make  the  culture  slightly  acid.  This 
is  in  accord  with  the  acidity  tests. 

In  observing  moribund  forms  disintegrate  (text  fig.  C,  1-12),  all 
food  yacuoles  were  seen  to  be  extruded,  the  body  flattened,  and  patho- 
logical vacuoles,  largely  water,  became  apparent  in  the  sulcal  axis. 
These  ruptured  leaving  the  body  very  irregular  in  shape.  Successive 
formation  of  these  vacuoles  finally  caused  complete  disintegration  of 


1919]     Rhodes :  Binary  Fission  m  Collodictyon  triciliatum  Carter    215 

the  body.  Even  then  the  nucleus  persisted  as  a  unit  for  some  two 
minutes,  when  the  nuclear  membrane  ruptured  and  the  karyosome 
alone  remained  as  a  unit,  retaining  its  form  for  over  half  an  hour. 
The  blepharoplast  persisted  as  an  irregular  granular  mass  surround- 
ing the  two  basal  granules.  As  long  as  this  mass  remained  as  a  unit, 
the  flagella  could  be  seen  to  wave  back  and  forth,  but  ceased  moving 
as  soon  as  the  mass  disintegrated. 

It  is  especially  noticeable  that  the  body  may  be  distended,  elon- 
gated, or  distorted  by  newly  engulfed  food  (pi.  9,  figs.  19-27).  It  may 
elongate  to  twice  its  normal  length  by  inclusions  of  filamentous  algae, 
desmids,  or  diatoms.  Such  elongation  is  usually,  though  not  always, 
anteroposteriorly.  The  modifications  due  to  inclusions  of  such  organ- 
isms as  Scenedesmus  or  Lagerheimia  I  have  already  mentioned. 
Chlorella  and  Protococcus  when  engulfed  were  arranged  peripherally 
within  the  vacuolated  cytoplasm,  just  underneath  the  surface  reticu- 
lum.  At  times  this  made  the  animal  appear  perfectly  green.  These 
frequently  popped  out  through  the  pellicle  and  when  first  observed 
made  me  think  of  zooids  from  flagellated  forms  in  multiple  fission. 
Such  a  condition  was  but  temporary,  however,  the  algae  either  being 
digested  for  food,  early  showing  the  surrounding  vacuole,  or  else,  I  am 
led  to  believe,  at  times  assuming  the  state  of  transient  symbiosis.  For 
three  months  such  a  congested  condition  was  both  typical  and  domi- 
nant. Seldom  was  Chlorella  digested  and  I  am  inclined  strongly  to 
the  idea  of  transient,  or  facultative  symbiosis. 

As  seen  in  the  living  state,  the  cytoplasm  consists  of  large,  hyaline 
vacuoles,  in  the  interstices  of  which  are  smaller  vacuoles,  and  the  spaces 
between  these  filled  with  granules  or  plasmosomes  in  a  fluid  matrix 
(pi.  8,  fig.  5).  The  periphery  of  each  vacuole  seems  to  consist  of  a 
definite  membrane,  more  the  result  of  a  turgid  surface  tension,  while 
the  interior  is  filled  with  a  hyaline  fluid. 

The  surface  of  the  cytoplasm  consists  of  smaller  vacuoles  with  a 
greater  number  of  granules.  The  arrangement  of  these  gives  the 
appearance  of  a  surface  reticulum,  with  the  larger,  deeper  vacuoles 
lying  against  or  within  it.  "When  disintegration  takes  place,  the 
pellicle  ruptures,  the  cytoplasm  goes  to  pieces  rapidly,  the  hyaline  fluid 
diffusing  into  the  water,  and  the  granules,  which  do  not  appear  nearly 
so  numerous  as  the  mass  of  the  organism  might  indicate,  are  scattered 
by  diffusion  currents. 

The  nucleus  possesses  no  vacuoles,  but  seems  to  consist,  much  as  the 
blepharoplast  and  the  immediately  surrounding  cytoplasm,  of  granules 


216  University  of  California  Publications  in  Zoology        [VOL-  I9 

in  a  fixed  matrix,  denser  and  more  refractive  than  the  cytoplasmic 
hyaloplasm.  In  the  resting  state  these  are  arranged  peripherally  just 
within  the  membrane.  The  nucleus  is  usually  disc-shaped,  being  flat- 
tened anteroposteriorly.  It  is,  when  seen  from  the  front  or  rear,  round, 
oval,  or  irregularly  elongated.  In  the  living  state,  and  when  intra- 
vitam  stains,  such  as  neutral  red  and  Bismarck  brown,  are  used,  there 
is  at  the  center  a  karyosome  which  seems  at  times  to  consist  of  closely 
compacted  granules  surrounded  by  a  light  hyaline  area  of  nuclear  sap 
in  which  there  are  no  granules,  the  periphery  of  which  seems  usually 
to  be  bounded  by  a  membrane.  When  the  nucleus  disintegrates  this 
granular  karyosome  persists  for  from  fifteen  to  thirty  minutes.  When 
stained  with  iron-alum  haematoxylin,  Delafield's  haematoxylin,  phos- 
photungstic  haematoxylin  and  others,  this  karyosome  appears  homo- 
geneous and  this  whole  mass  to  be  surrounded  by  the  hyaline  area,  thus 
giving  a  perfect  vesicular  nucleus. 

As  to  the  reticular  nature  of  its  protoplasm,  I  am  inclined  to 
regard  the  surface  of  the  vacuoles  as  modified,  perhaps  by  stress  or 
strain,  into  thickenings  or  longitudinal  strings  of  plasmosomes,  the 
interstices  of  the  larger  vacuoles  being  filled  with  still  larger  granules 
of  various  kinds,  food,  mitochondria,  plastids,  metaplastic  granules, 
and  foreign  organic  and  inorganic  bodies.  There  is  little  or  no  circu- 
lation of  vacuoles  or  protoplasm  visible  in  Collodictyon.  That  the 
nuclear  protoplasm  has  the  power  to  create  and  absorb  or  eliminate  a 
membrane,  metabolic  in  character,  around  the  microkaryosome,  will 
be  described  as  a  prophase  phemonenon ;  even  so,  a  cytoplasmic  vacuole 
may  be  bounded  by  a  definite  membrane,  kinetic  in  character,  which 
may  be  modified  so  as  to  appear  reticular  when  stained,  and  on  which 
are  accumulated  small  granules,  either  scattered  or  in  long,  bead-like 
strings.  All  of  this  is  in  addition  to  the  other  granules  which  may  be 
held  in  the  interstices  of  both  large  and  small  vacuoles. 

The  physical  nature  of  the  protoplasm  of  Collodictyon,  therefore, 
appears  to  be  a  fluid,  which  may  be  modified  by  metabolic,  kinetic  and 
other  life  processes  into  granular  or  reticular  variations,  these  how- 
ever, being  subject  to  reabsorption  into  a  hyaline  fluid,  or  becoming 
by-products,  such  as  plastids,  never  again  functioning  in  metabolism 
or  life  processes,  though  still  retained  in  the  cytoplasm. 

Besides  the  protoplasmic  vacuoles,  other  kinds  may  be  present. 
1.  Food  vacuoles,  which  may  contain  plants  or  animals  just  engulfed, 
or  which  may  be  very  old  and  alkaline  in  reaction,  simply  water  or 
digestive  spaces  in  which  little  remains.  These  may  flow  together 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    217 

when  Collodictyon  is  in  a  moribund  state,  giving  rise  to  what  France 
calls  water  vaeuoles.  2.  Water  vacuoles :  I  can  not  differentiate  these 
from  the  old  food  vacuoles  except  that  they  are  larger.  They  give 
similar  reaction  with  Congo  red.  Undoubtedly  they  are  pathological,  in 
the  sense  that  they  do  not  appear  except  in  moribund  condition.  The 
smaller  food  vacuoles  either  are  entirely  absorbed  or  their  contents 
are  extruded.  3.  In  the  moribund  state  the  simple  protoplasmic 
vacuoles  may  rupture  and  flow  together,  thus  creating  large  degenera- 
tion vacuoles,  indicative  of  a  quick  collapse. 

"Contractile  vesicles"  were  seen  and  described  by  Carter  (1865). 
He  did  not  figure  them,  however,  and  merely  indicated  that  their 
position  was  so  variable  that  he  evidently  failed  to  locate  them  for  his 
sketches.  Stein  (1878-83)  described  one  pulsating  vacuole  in  the 
anterior  end  and  figured  the  same.  Klebs  (1893)  indicated  one  in  the 
posterior  end  of  his  organism,  which  neither  France  nor  I  believe  to  be 
a  true  Collodictyon.  France  (1899)  found  one  at  the  anterior  end, 
about  6/tx  in  diameter,  which  pulsated  two  to  three  times  a  minute.  He 
says  that  it  is  near  the  nucleus,  but  very  hard  to  see  on  account  of 
the  numerous  granulations.  In  all  my  observations,  even  with  the 
compound  binocular  microscope,  I  have  failed  to  find  this  vacuole  or 
any  other  pulsating  vacuole.  The  individuals  were  often  free  from 
inclusions,  were  studied  when  actively  moving  about,  when  stained 
intra-vitam  with  neutral  red,  Bismarck  brown,  and  methylen  blue,  when 
retarded  by  nicotine,  Congo  red,  anilin  solution,  litmus  solution,  weak 
hydrochloric  acid  and  carbon  dioxide.  Several  times  in  watching  these 
forms  until  cytolysis  occurred,  I  have  seen  the  protoplasmic  vacuoles 
flow  together,  resembling  somewhat  contractile  vacuoles  discharging. 
I  am  sure  these  were  not  pulsating  vacuoles.  However  much  I  regret 
to  differ  from  previous  observers,  especially  France,  who  measured 
and  observed  the  period  of  pulsation,  I  am  constrained  to  believe  that 
in  the  Collodictyon  of  the  culture  under  discussion  there  is  no  con- 
tractile vacuole. 

France  (1899)  sums  up  most  satisfactorily  his  reasons  for  believing 
that  there  is  no  cuticle;  I  agree  with  him.  At  the  same  time,  the 
characteristic  form  is  such,  and  so  constant  for  the  individual,  especi- 
ally for  the  anterior  end,  that  I  am  convinced  there  is  a  periplast  or 
pellicle,  thin  and  undifferentiated,  of  smaller  vacuoles  or  homogeneous 
protoplasm.  This  must  be  a  coagulation  product.  It  at  least  is  rather 
impermeable  to  quick  action  of  many  chemicals,  especially  anilin  dyes. 

There  is  no  central  digestive  region,  but  food  vacuoles  are  held 


218  University  of  California  Publications  in  Zoology        [VOL.  19 

suspended  within  the  body,  at  times  rupturing  or  displacing  many 
protoplasmic  vacuoles.  Small  food  granules,  as  Chlorella,  are  arranged 
peripherally  just  underneath  the  periplast,  showing  that  the  suspension 
capacity  of  the  smaller  peripheral  vacuoles  is  greater  than  that  of  the 
larger  and  more  centrally  located  ones.  The  only  evidence  of  circula- 
tion of  food  vacuoles  is  that  most  of  the  undigested  products  are 
evacuated  from  the  posterior  portion  of  the  body. 

The  sulcus  has  been  described  in  discussing  the  various  modifica- 
tions of  form  but  its  chief  features  may  be  here  summarized.  It  cleaves 
one  side,  may  extend  anteriorly  so  as  to  cause  a  cordate  or  irregular 
depression  in  the  usual  oval  contour;  posteriorly  it  may  fade  out,  leav- 
ing the  general  shape  conical,  or  it  may  divide  the  body  into  two  cups, 
thus  giving  the  bifurcated  appearance ;  by  secondary  branches,  which 
also  tend  to  run  longitudinally,  there  may  be  produced  as  many  as 
five  posterior  cusps.  The  whole  of  the  sulcal  region  is  amoeboid  and 
functions  in  food  engulfing.  Much  of  the  irregularity  of  shape  is  due 
to  variations  in  this  region.  At  its  anterior  end  there  is  a  depression 
(pi.  9,  fig.  19)  which  may  function  as  a  cytostome  or  esophagus.  This 
seems  to  end  blindly,  having  no  connection  with  any  vacuole.  If  it 
may  at  all  be  regarded  as  a  cytostome,  it  is  most  primitive,  more 
potential  and  functional  than  structural. 

Collodictyon  possesses  a  true  vesicular  nucleus,  located  anteriorly 
near  the  base  of  the  flagella  and  may  be  either  centrally  located  or 
displaced,  usually  away  from  the  sulcus.  It  is  surrounded  by  a  distinct 
nuclear  membrane,  from  which  granular  cytoplasm  extends  out  into 
the  body  between  the  protoplasmic  vacuoles.  The  large  karyosome  is 
located  centrally  with  a  surrounding  hyaline  area. 

The  blepharoplast  is  located  anterior  to  the  nucleus,  at  the  base  of 
the  flagella  and  immediately  beside  the  depression  caused  by  the 
anterior  extension  of  the  sulcus.  When  killed  and  fixed  in  strong 
Flemming  and  stained  in  Bordeaux  red  and  iron  haematoxylin,  the 
blepharoplast  seems  to  consist  of  two  basal  granules  surrounded  by 
a  more  darkly  staining  granular  archoplasm  (pi.  9,  figs.  23-27).  It 
usually  appears,  especially  when  not  sufficiently  destained,  as  an 
irregular  chromatic  mass  in  which  are  embedded  the  two  basal  granules 
which  protrude  as  tubercles,  to  each  of  which  paired  flagella  are 
attached,  each  also  surrounded  by  a  granular  archoplasm  (pi.  12, 
figs.  19,  20).  It  is  probable  that  the  irregular  chromatic  mass  is, 
in  fact,  simply  a  lateral  view  of  an  archoplasmic  plate  or  cap  bound- 
ing the  granular  area  and  in  the  center  of  which  are  the  two  basal 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  tricilidtum  Carter    219 

granules.  There  is  evidence  in  vegetative  stages  for  a  faint  rhizoplast, 
probably  two  strands,  connecting  the  blepharoplast  to  the  nucleus,  and 
at  times  such  strands  can  easily  be  observed  (pi.  8,  fig.  13).  In 
division,  thickened  striations  and  fibers  connecting  the  blepharoplast 
and  nucleus  are  more  evident  than  at  other  times  (pi.  11,  figs.  40,  44). 
These  no  doubt  are  rightly  interpreted  as  dividing  rhizoplasts. 


Normally  Collodictyon  is  pelagic,  floating  near  the  surface  of  the 
water  in  the  aquarium,  but  at  all  times  of  the  day  and  at  all  tempera- 
tures tested  and  under  all  conditions  of  light  and  darkness  some  have 
been  found  scattered  throughout  the  aquarium.  In  a  free  drop  of 
water  on  a  slide  they  tend  to  stratify  near  the  substrate,  but  in  a 
hanging  drop  they  swim  about  throughout  the  drop,  only  occasionally 
accumulating  near  the  slide.  In  the  aquarium  they  rest  both  in  the 
direct  sunlight  and  also  in  shaded  portions;  but  there  is  a  marked 
tendency  to  gather  nearest  the  source  of  light.  When  there  are 
abundant  algae  floating  on  the  surface  of  the  aquarium,  they  can  be 
found  at  or  just  beneath  the  surface  and  then  there  is  a  region  of 
scant  distribution  below  which  they  tend  to  accumulate  in  greatest 
abundance.  This  may  be  on  account  of  a  superabundance  of  oxygen 
or  to  too  great  heat  at  the  surface,  due  to  the  absorption  of  heat  by 
the  algae  and  the  surface  reflection. 

As  to  the  association  of  Collodictyon  with  water  pollution  and  pools 
in  which  decay  has  been  or  is  progressing  rapidly,  I  am  less  positive 
in  my  convictions  than  France  (1899)  seemed  in  his  conclusions.  My 
own  observations  have  been  that  Collodictyon  can  not  live  where  there 
is  a  great  amount  of  decay.  They  are  holozoic,  however  (with  the 
possible  exception  of  times  when  there  is  a  symbiotic  association  with 
Chlorella),  and  live  on  Protozoa  and  algae  wrhich  are  associated  with 
decay.  Their  own  life  seems  far  removed  from  saprozoic  nutrition 
and  I  find  little  in  the  rate  of  multiplication  that  tends  to  confirm 
such  a  supposition  or  conclusion.  As  to  the  fact  that  they  were  found 
in  pools  where  disintegration  was  rapidly  increasing  or  at  a  maximum, 
I  am  not  in  a  position  to  question  except  from  cultural  experiments, 
in  which  other  factors  might  have  played  a  determining  part;  but  I 
urge  this  same  factor,  unknown  as  it  is,  in  explanation  of  France's 
observation.  France's  argument  that  Euglena  is  its  chief  and  only 


220  University  of  California  Publications  in  Zoology        [VOL.  19 

source  of  food  will  not  hold,  since  I  find  engulfed  Ulothrix,  dinoflagel- 
lates,  Pandorina,  Gonium,  Chlorella,  etc.,  more  common  in  my  aqua- 
rium than  Euglena.  I  do  find  the  species  collectively  a  ' '  lover  of  pure 
water,"  thriving  in  sunshine  and  in  a  balanced  aquarium.  I  can 
therefore,  at  least  conclude  that  increasing  or  maximum  decay  is  not 
essential  to  the  life  of  the  organism,  and  that  C  otto  diet  yon  is  not  a 
determining  factor  in  water  pollution. 

When  free  swimming,  Collodictyon  moves  forward  by  beautiful 
lashings  of  the  flagella  in  true  tractellar  style,  the  flagella  undulating 
as  the  animal  circles  about.  It  may  also  move  backward  by  the 
anterior  adaxial  action  of  the  flagella,  but  only  seems  to  do  so  in  an 
avoiding  reaction.  It  rotates  on  its  longitudinal  axis  more  frequently 
clockwise,  but  seemingly  without  cause  or  provocation  may  reverse 
and  rotate  counter-clockwise.  The  flagella  may  beat  back  on  all  sides 
of  the  body,  closely  appressed  to  the  pellicle.  It  frequently,  wrhen 
near  the  substratum,  attaches  itself  by  its  flagella  and  rotates  clock- 
wise about  its  longitudinal  axis.  As  to  the  explanation  of  this  I  am 
in  doubt.  I  am  inclined  to  believe  it  simply  a  thigmotactic  response, 
possibly  combined  with  positive  geotropism ;  but  in  swimming  through 
the  water  when  nearing  an  object  it  touches  it  with  its  flagella  and 
usually  passes  to  one  side  or  jostles  the  object  out  of  the  way  if  small 
enough. 

In  its  feeding  habits,  Collodictyon  is  most  interesting.  "When  hungry, 
it  can  be  distinguished  from  moribund  stages  in  which  all  food  is 
extruded  by  pseudopodial  projections  from  the  lateral  groove  or  sulcal 
region  (text  fig.  A,  1-5).  France  emphasized  the  adhering  engulfing 
process,  speaking  little  of  the  pseudopodia.  I  wish  to  emphasize  these 
pseudopodia,  for  I  observe  that  they  function  actively  whenever  the 
organism  is  seeking  food.  At  these  times  when  coming  in  contact  with 
Protozoa  or  algae  which  it  may  use  for  food,  they  are  wafted  to  the 
sulcal  region  by  the  flagella,  or  else  Collodictyon  aligns  itself  alongside  of 
its  prey  with  the  pseudopodia  in  contact.  If  an  elongated  filamentous 
alga  is  to  be  engulfed,  the  relationship  between  the  two  is  nearly  always 
with  the  alga  lying  in  the  groove  longitudinally;  but  I  have  noticed 
with  diatoms  that  they  just  as  frequently  are  engulfed  by  the  end.  Both 
the  flagella  and  the  pseudopodia  appear  sensitive  to  food  stimulus  and 
usually  there  is  coordination  between  the  protoplasm  of  the  sulcal  region 
and  the  flagella,  though  there  seems  to  be  no  mechanism  for  this  other 
than  the  primitive  characteristics  of  the  protoplasm.  The  process  of  the 
organization  of  a  food  vacuole  is  a  combination  of  circumvallation  and 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    221 

circumfluence  (Minchin,  1912,  p.  189).  The  food  is  frequently  sur- 
rounded by  engulfing  protoplasm  of  the  pseudopodium  before  it  begins 
to  sink  into  the  vacuolated  body,  but  the  latter  process  always  takes 
place  and  at  such  times  there  may  be  a  considerable  shifting  of  internal 
vacuoles.  Once  I  noticed  the  rupture  of  several  vacuoles  on  the  engulfing 
of  a  very  large  Pandorina  morum,  undoubtedly  explicable  by  the  move- 
ments of  the  captured  organism.  Collodictyon  may  engulf  much  food, 
almost  as  much  as  its  own  size  and  still  appear  very  little  larger. 
France  cites  an  instance  where  ten  Euglena  minima  and  Chlamydo- 
monas  filled  up  the  interior  of  Collodictyon.  Its  normal  cytoplasmic 
vacuoles  must,  therefore,  not  only  be  displaced,  but  also  ruptured 
and  the  food  vacuole  take  the  place  of  one  or  more  of  these.  There  is 
always  a  slight  water  ring  surrounding  the  new  food  vacuole,  but  as 
it  grows  older  this  seems  to  be  supplanted  by  a  protoplasmic  film 
coming  directly  in  contact  with  the  substance  being  digested.  Tests 
with  Congo  red  and  litmus  bring  out  these  differences  intra-vitam. 
In  the  use  of  the  former,  the  food  vacuoles  present,  for  some  time 
appear  red,  thus  indicating  alkalinity,  but  the  small  vacuoles  in  final 
stage  of  digestion  are  blue,  indicating  acidity.  Litmus  did  not  yield 
such  good  results,  though  the  water  film  was  shown  up  very  well. 
Collodictyon  has  been  seen  to  be  engulfed  by  a  larger  form  of  its  own 
species.  It  is  not  only  a  cannibal,  but  is  very  voracious,  and  almost 
omnivorous.  Peridinium,  Pandorina,  Euglena,  Amoeba,  Chlamydo- 
monas,  a  ciliate  (presumably  Colpidium),  Pediastrum,  Scenedesmus, 
Lagerheimia,  Ulothrix,  Chlorella,  Navicula,  and  Gonium,  have  been 
observed  being  ingested  or  in  food  vacuoles  within  the  body  (pi.  9, 
figs.  19-27). 

MITOSIS 

RESTING  STAGE 

In  the  normal  nucleus  of  Collodictyon  in  the  resting  stage  the 
following  organelles  appear  to  play  important  roles.  The  nucleus  is 
surrounded  by  a  nuclear  membrane,  which  stains  very  lightly  with 
iron  haematoxylin,  but  a  dark  red  with  acid  fuchsin  and  safranin. 
The  shape  of  the  nucleus  is  variable  but  typically  is  an  ovoid  flattened 
on  the  posterior  side  or  anteroposteriorly,  the  longitudinal  axis  lying 
perpendicular  to  the  major  axis  of  the  cell.  This  nucleus  is  vesicular. 
The  central  karyosome  measures  2  to  3/x,  in  diameter  and  appears 
homogeneous  with  all  stains  except  Bordeaux  red,  iron  haematoxylin, 
and  neutral  red  used  intra-vitam,  with  which  it  appears  granular; 


222  University  of  California  Publications  in  Zoology        [VOL.  19 

with  safranin,  the  periphery  appears  to  contain  masses  of  granules 
of  chromatin  while  the  center  is  homogeneous  and  more  or  less  trans- 
lucent. Surrounding  this  karyosome  is  a  hyaline  area,  measuring 
from  1  to  3/i  in  width,  which  is  always  transparent  and  takes  none 
of  the  nucleus  stains  but  is  lightly  colored  with  eosin  and  acid  fuchsin 
about  the  same  as  the  cytoplasm.  Around  this  there  is  a  peripheral 
area,  varying  in  width  and  definiteness,  in  which  irregular  chromatin 
masses,  small,  variable  in  size,  number  and  shape,  occur.  This  area 
is  from  y2  to  3/A  in  width.  It  is  surrounded  by  the  nuclear  membrane. 

The  chromatin  material  is  frequently  encrusted  upon  the  nuclear 
membrane  in  the  resting  stages  of  the  nucleus.  Much  chromatin  is 
accumulated  in  masses  scattered  peripherally  between  the  hyaline 
area  and  the  membrane,  at  times  (presumably  when  anabolic  processes 
greatly  predominate  over  the  katabolic)  reducing  the  hyaline  area 
to  a  minimum.  But  the  largest  amount  of  the  chromatin  is  found  in 
the  karyosome  which  stains  deeply  with  all  nuclear  stains.  Thus  the 
chromatin  encrusted  upon  the  membrane,  that  occurring  in  the  peri- 
pheral zone,  and  that  making  up  the  karyosome,  or  the  larger  part 
of  it,  all  has  to  be  accounted  for  later  in  mitosis. 

The  blepharoplast,  located  at  the  anterior  end,  is  irregular  in  size 
and  shape.  It  consists  of  a  mass  of  chromatoidal  protoplasm  which 
tends  to  become  stellate  in '  shape,  much  like  a  nerve  cell,  deeply 
staining  strands  extending  out  into  the  cytoplasm  between  the 
vacuoles  (pi.  9,  fig.  20).  Embedded  in  this  blepharoplast  are  two 
basal  granules,  which  are  distinctly  red  when  stained  with  safranin, 
gentian- violet,  orange  G,  and  acid  fuchsin.  From  each  of  these 
basal  granules  two  equal  flagella  arise.  From  the  blepharoplast, 
probably  from  each  of  the  basal  granules,  arise  the  two  rhizoplasts, 
which  extend  as  strands  from  the  chromatoidal  mass,  but  instead  of 
remaining  upon  the  surface  as  the  other  strands  do,  run  interiorly 
to  the  nucleus,  enlarging  at  the  nuclear  membrane  into  a  minute 
granule.  In  some  instances  the  nuclear  membrane  is  drawn  up  at 
the  point  of  attachment  of  the  extranuclear  rhizoplast.  In  several 
instances  (pi.  7,  fig.  1),  an  intranuclear  rhizoplast  seems  to  penetrate 
the  membrane  and  run  to  the  central  karyosome. 

The  cytoplasm  immediately  surrounding  the  nucleus  is  closely 
appressed  to  the  membrane,  making  it  difficult  at  times  to  distinguish 
the  latter.  It  is  denser  and  more  granular,  and  extends  out  into  the 
body  in  strands  which  lie  between  the  protoplasmic  vacuoles.  It 
stains  much  as  the  peripheral  nuclear  area  with  iron  haematoxylin, 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    223 

but  is  not  so  evident  with  safranin;  gentian-violet,  orange  G,  or  Mai- 
lory's  modified  connective  tissue  stain.  This  area  of  cytoplasm  is 
not  differential  cytoplasm,  for  the  interstitial  material  between  or 
bounding  the  protoplasmic  vacuoles  throughout  the  cytoplasm  stain 
thus  deeply  with  all  nuclear  as  well  as  plasma  stains  that  I  have  tried. 
It  seems,  therefore,  to  be  merely  the  cytoplasm  in  which  the  nucleus 
is  suspended,  being  largely  granular  instead  of  vacuolar.  This 
denser  cytoplasmic  area  just  surrounding  the  nucleus  is  a  condition 
of  the  resting  nucleus  and  not  a  mitotic  phenomenon. 

The  state  of  the  microkaryosome  is  of  help  in  determining  the 
progress  of  mitosis  especially  of  the  prophase;  but  the  expanding  of 
the  kinetic  membrane  is  the  best  criterion  of  this.  A  chromatin  halo 
inside  of  the  nucleus  usually  accompanies  this. 

When  division  begins,  or  very  soon  thereafter,  all  undigested  food 
particles  and  other  foreign  bodies  are  extruded.  There  is  no  round- 
ing up  of  the  cell,  the  characteristic  shape  being  retained  throughout 
mitosis.  I  have  never  seen  pseudopodia  or  amoeboid  protrusions  from 
the  sulcal  region  in  division  stages. 


UNEQUAL  CONSTRICTION  OF  THE  KARYOSOME 

Preliminary  to  true  mitosis,  the  karyosome  usually  elongates  and 
constricts  into  a  dumb-bell  shape  with  the  knobs  of  unequal  size. 
These  pull  apart  until  connected  only  by  a  strand,  which  finally 
breaks,  accomplishing  an  unequal  or  differential  division  of  the 
karyosome  (pi.  10,  figs.  29,  30).  The  resulting  large  and  small 
daughter  karyosomes  are  not  equivalents  either  in  size  or  behavior, 
and  by  reason  of  their  size  I  shall  designate  them  macrokaryosomes 
and  microkaryosomes  respectively  (pi.  10,  figs.  31,  32). 

During  this  preliminary  unequal  constriction  of  the  karyosome, 
I  have  been  unable  to  detect  any  change  in  the  blepharoplast,  which 
consists  of  two  basal  granules  surrounded  by  granular  archoplasm. 
I  have  not  seen  anything  resembling  a  splitting  of  the  rhizoplast  at 
either  end.  The  flagella  are  still  four  in  number  at  this  stage  (pi.  10, 
figs.  28-31,  34,  36). 

The  macrokaryosome  is  homogeneous  in  appearance  with  all  stains 
used  and  contains  no  residual  body.  It  may  be  regarded  as  consist- 
ing of  plastin  impregnated  with  chromatin.  Its  behavior  is  passive. 
It  loses  its  surrounding  hyaline  area,  and  may  round  up  or  form  a 
crescentic  mass  around  and  outside  of  the  kinetic  membrane.  It  is 


224  University  of  California  Publications  in  Zoology        [VOL.  19 

then  pushed  by  this  expanding  membrane  out  to  the  periphery  of 
the  nucleus,  where  it  reposes  in  a  niche  of  the  nuclear  membrane,  but 
separated  from  the  mitotic  area  within  by  the  persistent  kinetic 
membrane  (pi.  11,  figs.  38,  44). 

It  has  been  found  on  several  occasions  (pi.  11,  fig.  43)  to  break  up 
and  form  an  intranuclear  chromatin  cloud.  Even  where  it  has  been 
traced  repeatedly  to  its  position  near  the  nuclear  membrane,  I  have 
never  located  it  or  any  similar  chromatin  mass  outside  the  nucleus. 
In  some  instances  it  seems  that  the  cytoplasm  just  around  the  nucleus 
is  more  deeply  stained  by  a  chromidial  cloud  as  though  the  macro- 
karyosome  or  a  part  of  it  were  extruded  in  fine  granules.  Such  is 
undoubtedly  its  fate  in  many  individuals.  But  much  evidence  points 
to  the  gradual  absorption  of  the  macrokaryosome  in  situ  in  some 
instances  within  the  nuclear  membrane,  with  the  formation  of  an 
intranuclear,  intrakinetic  membrane  chromatin  cloud  (pi.  10,  figs.  35, 
36,  pi.  11,  figs.  37,  38,  41,  42,  44,  45).  There  is  some  evidence  (pi.  11, 
fig.  46,  pi.  12,  fig.  48)  that  it  may  in  other  instances  persist  and  pass 
over  to  one  of  the  daughter  nuclei  without  complete  dissolution. 
There  is  no  evidence  for  its  splitting  or  division  on  the  equatorial 
plate.  Its  behavior  seems  dependent  in  some  way  upon  the  meta- 
bolic equilibrium  of  the  nucleus  and  cytoplasm.  Its  significance, 
regarding  possible  relations  with  the  parabasal  body  of  parasitic 
flagellates,  the  macronucleus  of  ciliates,  Hertwig's  theory  of  tropho- 
chromatin  and  idiochromatin,  and  Hartmann's  binuclear  theory,  in 
so  far  as  flagellates  are  concerned,  will  be  taken  up  in  subsequent 
discussion. 

Individuals  in  evident  stages  of  the  prophase  have  been  observed 
in  which  there  is  a  total  absence  of  any  evidence  of  a  constriction 
of  the  karyosome.  The  kinetic  karyosome  (microkaryosome)  entering 
into  mitosis  may  likewise  on  rare  occasions  be  larger  than  the  other 
mass,  the  passive  macrokaryosome. 

MITOSIS 

"With  the  organization  of  the  microkaryosome  mitosis  begins. 
Binary  fission  by  longitudinal  division  seems  to  be  initiated  within 
this  karyosome.  This  forms  about  itself  the  kinetic  membrane,  which 
continues  to  expand  until  it  becomes  commensurate  with  the  nuclear 
membrane.  The  faint  rhizoplasts  extend  from  the  kinetic  membrane 
which  surrounds  the  organizing  microkaryosome,  through  the 


Rhodes:  Binary  Fission  in  Collodictyon  trieiliatum  Carter     225 

peripheral  granular  area  to  the  nuclear  membrane;  from  here  they 
pass  through  the  intervening  cytoplasm  to  the  basal  granules  within 
the  blepharoplast.  The  rhizoplasts  are  not  sufficiently  prominent  to 
be  evident  to  the  uninitated  eye.  They  may  easily  be  confused  with 
the  attenuated  strands  from  the  blepharoplasts  radiating  out  into  the 
surface  cytoplasm. 

Two  small  granules  have  been  observed  just  at  the  point  where 
the  rhizoplasts  enter  the  nuclear  membrane  on  their  way  to  the  central 
karyosome  (pi.  8,  figs.  9,  13).  In  early  and  late  prophase  stages 
(pi.  14,  fig.  75)  these  separate  and  the  nuclear  membrane  appears 
heavier  or  thicker  between  these  points  in  comparison  with  the  rest 
of  the  membrane,  as  though  an  extranuclear  paradesmose  were  form- 
ing. In  a  lately  discovered  metaphase  (pi.  14,  fig.  78)  this  paradesmose 
is  well  formed,  connecting  the  polar  ends  of  the  spindle.  In  one 
particularly  favorable  anaphase  (pi.  14,  fig.  83)  granules  of  consider- 
able size  are  located  at  the  polar  ends  of  the  daughter  chromatin 
masses  and  these  are  connected  by  a  heavy  paradesmose  upon  the 
nuclear  wall. 

This  evidence  points  definitely  to  the  presence  of  an  extranuclear 
division  center  or  centrosome.  Such  is  typical  of  parasitic  poly- 
mastigotes  (Kofoid  and  Christiansen,  1915,  Kofoid  and  Swezy,  1915a, 
1915&,  Swezy,  1915,  Boeck,  1917)  and  may  be  considered  typical  of 
polymastigotes  in  general.  In  this  case,  however,  the  blepharoplast 
and  centrosome  are  separate,  the  latter  adhering  to  the  nuclear 
membrane. 

The  rhizoplasts  split  first  at  the  end  near  the  nuclear  membrane, 
presumably  with  the  division  and  separation  of  the  centrosomes.  The 
split  extends  anteriorly,  giving  the  appearance  of  a  V-shaped  striated 
region  (pi.  8,  fig.  13).  Finally  with  the  separation  and  division  of 
the  basal  granules  of  the  blepharoplast  (pi.  8,  fig.  9)  the  rhizoplasts 
appear  distinct  and  their  points  of  contact  with  the  nuclear  mem- 
brane become  farther  apart. 

In  justice  to  truth,  it  must  be  said  that  the  problem  of  the  division 
center  has  been  full  of  difficulties.  The  material  in  hand  is  of  such 
a  nature  that  the  possibility  of  error  must  not  be  overlooked.  The 
apparent  points  of  contact  of  the  rhizoplast  with  the  nuclear  mem- 
brane are  exceedingly  faint.  The  extranuclear  cytoplasmic  granules 
and  vacuoles  and  the  intranuclear  chromatin  encrusted  in  granules 
upon  the  nuclear  membrane,  which  are  connected  in  prophase  by 
somewhat  chromatic  lines,  are  exceedingly  confusing.  This  renders 


226  University  of  California  Publications  in  Zoology        [VOL.  19 

the  above  interpretation  still  tentative.  Much  work  is  still  needed 
upon  CottocKctyon  and  related  forms  to  clear  up  fully  the  question 
of  the  division  center. 

The  time  at  which  the  blepharoplast  divides  has  not  been  definitely 
determined.  There  is  evidence  of  its  division  as  early  as  the  middle 
of  the  prophase  (pi.  11,  figs.  40,  40a).  It  seems,  from  the  figures 
just  referred  to,  that  the  method  is  one  of  doubling  of  the  basal 
granules,  thus  making  two  pairs,  which  gradually  separate  (pi.  11. 
fig.  46,  pi.  12,  figs.  48,  53,  54).  No  splitting  of  the  flagella  has  been 
observed,  but  since  only  equal  flagella  have  been  found  in  these 
stages,  it  seems  safe  to  conclude  that  the  flagella  split  longitudinally 
or  new  ones  grow  out  at  about  the  same  time  as  the  doubling  of  the 
paired  basal  granules.  At  the  metaphase  the  doubling  is  complete 
(pi.  12,  fig.  48). 

PROPHASE 

"With  the  unequal  constriction  of  the  karyosome,  sometimes  even 
before  this  differential  division  has  been  completed,  the  microkaryo- 
some  organizes  about  itself  a  membrane,  which  seems  to  have  a  kinetic 
or  metabolic  function  and  which  I  shall  designate  as  the  kinetic 
membrane.  The  macrokaryosome  is  passive  in  behavior  and  remains 
outside  of  this  active  membrane.  The  kinetic  membrane  does  not 
simply  bound  the  hyaline  area,  but  is  almost  surrounded  by  such  a 
zone  (pi.  10,  fig.  32).  At  first  the  space  between  the  microkaryosome 
and  the  membrane  is  hyaline,  but  it  is  soon  filled  with  a  dense 
chromatin  cloud  (pi.  11,  figs.  37,  38,  41,  42,  44).  This  kinetic  mem- 
brane seems  somewhat  less  chromatic  than  the  nuclear  membrane. 
Usually  it  is  spherical  or  irregularly  globular,  but  in  two  or  three 
instances  angular,  almost  polygonal  (pi.  10,  figs.  32,  33),  which  is 
probably  an  artifact.  As  it  enlarges,  however,  it  may  elongate  and 
its  shape  become  modified  by  the  organizing  spindle. 

When  the  organization  of  the  microkaryosome  is  begun,  the 
chromatin  outside  the  kinetic  membrane  tends  to  accumulate  in 
granules  or  masses  wrhich  are  linked  together  by  slightly  chromatic 
strands  (pi.  10,  figs.  30,  32,  36).  Much  of  it  is  encrusted  upon  the 
nuclear  membrane  (pi.  10,  fig.  32)  ;  much  forms  immediately  around 
the  hyaline  area  surrounding  the  kinetic  membrane  (pi.  10,  fig.  30), 
frequently  also  about  the  macrokaryosome  (pi.  11,  fig.  40).  The 
whole  peripherial  zone  becomes  thus  involved  and  with  the  expansion 
of  the  active  hyaline  area  is  more  and  more  encroached  upon  until 


Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter     227 

only  the  chromatin  encrusted  upon  the  nuclear  membrane  remains 
outside  of  it.  As  to  the  behavior  of  this  peripheral  chromatin,  there 
is  some  doubt.  It  may  pass  into  solution  and  become  a  part  of  the 
metaphase  chromosomes,  or  spread  out  upon  the  nuclear  membrane, 
making  this  appear  heavier  and  darker,  or  it  may  be  extruded  into 
the  cytoplasm.  There  is  an  indication  in  a  few  individuals  of  a 
peculiar  splitting  of  peripheral  encrusted  chromatin  bodies  (pi.  11, 
fig.  46).  I  can  not  verify  this  as  a  regular  occurrence  nor  can  I 
regard  it  as  typical.  This  splitting  is  prior  to  the  metaphase  and 
may  be  closely  correlated  with  the  precocious  splitting  of  the  seg- 
mented spireme  (pi.  12,  fig.  47). 

The  microkaryosome  elongates  and  divides,  the  separation  being 
characterized  by  connecting  fibrils  somewhat  resembling  spindle 
fibers,  rather  than  a  dumb-bell  constriction  as  in  differential  division 
of  the  primary  karyosome  (pi.  10,  figs.  34,  35,  36).  A  chromatin  cloud 
forms  immediately  around  this  elongating  microkaryosome  and  fills 
up  the  intervening  space,  almost  obliterating  the  fibers  (pi.  11,  figs.  37, 
38).  This  cloud  expands  until  the  whole  area  within  the  kinetic 
membrane  becomes  diffusely  filled  with  fine  granules. 

This  early  microkaryosome  organization  is  exceedingly  complex 
for  microscopic  analysis,  but  it  soon  becomes  evident  that  instead  of 
having  divided  simply  into  two  masses,  the  microkaryosome  is  under- 
going a  segmenting  process  (pi.  11, 'figs.  39,  40,  41,  42,  44,  45),  pre- 
liminary to  a  final  prophase  spireme  (pi.  12,  fig.  47).  The  first  division 
is  followed  by  a  second  elongation  of  each  mass,  apparently  passing 
through  a  tripod  and  ring  stage,  in  time  forming  two  crescentic 
masses  or  a  segmented  skein  (pi.  11,  figs.  40,  41,  42,  44).  This  retains 
terminal  chromatin  masses  or  knobs  which  probably  form  the  basic 
elements  of  the  future  chromosomes.  The  next  phase  is  a  longitudinal 
splitting  of  each  segment  (pi.  11,  fig.  45).  If  all  terminal  knobs 
divide  at  this  time,  eight  chromatin  masses  would  result  and  this 
would  probably  determine  the  correct  count  of  chromosomes.  It  is 
possible  that  one  of  the  four  terminal  knobs  fails  to  divide,  and  this 
would  give  but  seven  chromatin  masses — as  many  chromosomes  as  I 
have  been  able  to  count  (pi.  12,  fig.  50).  Such  a  phenomenon  is 
common  in  mitoses  of  higher  animals  (Wenrich,  1916;  Carothers, 
1917),  but  it  must  be  admitted  that  the  evidence  here  is  not  con- 
clusive (pi.  11,  fig.  45).  The  middle  and  final  prophase  stages  are 
characterized  by  an  active  organization  of  chromatin  upon  the 
segmenting  skein.  That  there  is  some  chromatin  in  the  original 


228  University  of  California  Publications  in  Zoology        [VOL.  19 

microkaryosome  there  can  be  little  doubt  and  this  seems  to  persist  as 
the  terminal  knobs  to  the  skein  segments. 

That  all  the  chromatin  entering  into  the  formation  of  the  chromo- 
somes can  not  possibly  be  of  the  original  microkaryosome  is  obvious. 
Considering  the  average  individuals,  the  average  size  of  the  micro- 
karyosomes  when  separated  from  the  macrokaryosomes  may  be  esti- 
mated at  about  1.5  to  2/u,  in  diameter.  The  size  of  six  of  the  chromo- 
somes may  relatively  be  estimated  at  0.75  x  1.5/u.  each,  the  small  one 
being  only  half  as  large  (pi.  12,  fig.  50).  All  other  chromatin  is  out- 
side the  kinetic  membrane  and  it  does  not  seem  probable  that  it  could 
go  through  as  granules  or  mass  units,  since  the  area  immediately 
around  the  kinetic  membrane  is  hyaline  and  in  a  state  of  solution, 
while  the  area  within  becomes  filled  with  a  dense  chromatin  cloud, 
and  the  only  chromatin  masses  consist  of  the  persisting  and  re- 
organizing elements  of  the  microkaryosome.  It  appears,  therefore, 
that  there  is  a  solvent  action  within  the  hyaline  area  around  the 
membrane  and  that  chromatin  from  the  granules  in  the  peripheral 
zone,  possibly  from  the  macrokaryosome,  and  probably  from  that 
encrusted  upon  the  nuclear  membrane,  is  dissolved  and  passed  through 
the  kinetic  membrane  by  diffusion  and  enters  into  the  composition 
of  the  chromosomes.  This  demands  a  higher  pressure  from  without, 
which  can  easily  be  accounted  for  by  the  chromatin  within  the  mem- 
brane being  condensed  and  precipitated  upon  the  achromatic  linin 
fibers  of  the  skein.  When  the  kinetic  membrane  has  expanded  to  the 
limits  of  the  nuclear  membrane,  this  early  phase  of  a  segmented 
spireme  (pi.  12,  fig.  49)  finally  organizes  into  a  skein  resembling  a 
more  or  less  continuous  ribbon,  with  chromatin  granules  embedded 
upon  it.  This  seems  to  be  accomplished  by  a  longitudinal  separation 
of  the  segments,  the  terminal  knobs  especially  showing  this  division. 
A  final  split  involving  the  formation  of  sixteen  chromatin  masses 
(pi.  12,  fig.  49)  may  be  found  and  may  be  regarded  as  the  precocious 
splitting  of  the  definitive  chromosomes.  From  these  chromatin  masses 
which  are  already  arranged  in  an  equatorial  belt  the  seven  or  eight 
chromosomes  of  the  equatorial  plate  are  finally  organized  (pi.  12,  fig. 
50),  probably  re-fused  by  a  telosynaptic  process. 

The  interpretation  of  a  segmenting  spireme  seems  necessary 
because  of  the  fact  that  its  elements  seem  to  be  directly  produced 
by  the  early  division  and  organization  of  the  microkaryosome,  this 
being  evident  before  the  metabolic  membrane  has  expanded  to  its 
final  proportions.  This  spireme  frequently  has  the  appearance  of  a 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  tricilidtum  Carter    229 

tripod,  ring,  or  double  crescent  (pi.  11,  figs.  39,  40,  41,  42,  44).  I 
found  one  difficulty  of  technique  here  hard  to  overcome.  The 
chromatin  cloud  is  usually  so  dense  that  whenever  this  is  sufficiently 
destained  to  see  the  skein,  this  latter  is  rendered  unfit  for  detailed 
interpretation. 

In  Phrynotettix  (Wenrich,  1916,  p.  112)  plasmosomes  may  change 
into  polar  granules  of  chromosomes  and  vice  versa. 

One  of  the  most  puzzling  problems  that  cytologists  have  to  deal  with  is  the 
behavior  and  function  of  the  so-called  "plasmosomes"  or  "nucleoli."  They 
apparently  exhibit  such  a  varietv  of  reactions  to  methods  of  technique,  and 
exhibit  such  varying  relationships  to  other  structures  in  the  cell,  that  it  is 
almost  hopeless  even  to  attempt  to  classify  them.  That  they  play  some  import- 
ant role  in  the  physiology  of  the  cell,  there  is  not  the  slightest  doubt,  but  what 
that  role  is,  'or  what  relation  they  bear  to  the  question  of  chromosome-individu- 
ality, are  problems  that  are  far  from  a  solution  at  the  present  time. 

There  is  hardly  a  close  analogy  between  Phrynotettix  and  Collo- 
dictyon, but  here  they  offer  a  most  interesting  comparison.  The 
terminal  knobs  of  the  segmenting  skein  of  Collodictyon  lend  them- 
selves to  the  interpretation  that  they  are  elements  at  least  of  the 
chromosomes.  In  Phrynotettix  the  individuality  of  the  chromosomes 
is  traced  by  similar  chromatin  masses  which,  however,  are  not  all 
terminal  and  several  of  which  may  enter  into  the  composition  of  a 
chromosome. 

The  blepharoplast  divides  during  the  middle  or  final  prophase. 
The  rhizoplasts  thicken  and  evidently  split  soon  after  the  kinetic 
membrane  begins  to  expand  (pi.  11,  fig.  40).  The  spindle  is  not 
organized  until  after  the  spireme  and  skein  are  far  advanced.  The 
cytoplasm  immediately  surrounding  the  nucleus  may  become  darker, 
due  to  the  presence  of  a  chromidial  cloud  from  extruded  chromatin. 
The  nuclear  membrane  persists.  The  protoplasmic  vacuoles  may  or 
may  not  be  large.  They  are  as  normal  as  in  the  vegetative  stages 
and  their  variations  are  largely  the  result  of  food  vacuoles  extruded 
at  the  beginning  of  division.  If  one  so  cares,  the  prophase  may  be 
regarded  as  beginning  with  the  unequal  constriction  of  the  karyosome. 
I  have  separated  these  stages  arbitrarily  for  advantages  of  analysis. 

METAPHASE 

The  nucleus  becomes  filled  with  a  perfect  spindle,  which  lies  at 
right  angles  to  both  the  major  axis  of  the  cell  and  to  the  sulcal  axis, 
usually  on  one  side  or  the  other  of  the  sulcus.  The  chromosomes  are 
now  seven  or  eight  in  number  (pi.  12,  fig.  50).  There  is  a  general 


230  University  of  California  Publications  in  Zoology        [VOL.  19 

uniformity  of  size  and  shape,  being  ovoid,  from  1.5  to  2//,  in  length, 
0.5  to  0.75/x,  wide;  with  one  exception,  namely  that  one  chromosome 
is  but  half  so  long  and  hardly  so  wide.  These  are  arranged  equatori- 
ally  with  very  slight  tendency  to  V-shape  or  crescent-shape.  Their 
elongated  axes  are  meridional  to  the  spindle. 

In  division  (pi.  12,  fig.  50)  all  the  chromosomes  but  one  in  this 
spindle  appear  to  have  parted  transversely.  The  spindle  fibers  are 
attached  to  the  ends  and  not  to  the  centers  or  sides.  This  parting 
may  be  fundamentally  similar  to  the  parting  of  the  chromosomes  as 
found  by  Tschenzoff  (1916)  in  Euglena.  The  precocious  splitting 
is  evidently  not  so  far  removed  from  the  metaphase,  however,  since 
in  Euglena  it  apparently  takes  place  in  the  preceding  telophase  of 
the  parental  individual,  wThile  in  Collodictyon  it  takes  place  no  farther 
back  than  the  late  prophase  just  preceding  the  metaphase. 

In  the  most  satisfactory  metaphase  I  have  found  (pi.  12,  fig.  50), 
the  small  chromosome  has  not  as  yet  divided.  No  constriction  can 
be  found  in  it  in  this  figure.  It  may  best  be  interpreted  as  a  lagging 
chromosome.  In  such  a  case  it  would  probably  divide  later  on  in  the 
metaphase  or  early  anaphase,  though  there  is  no  available  material 
to  determine  this  matter. 

In  one  anaphase  (pi.  12,  fig.  51)  there  are  obviously  unequal 
chromatin  masses.  These  are  either  so  deeply  stained  as  to  prevent 
an  accurate  chromosome  count  or  else  the  chromosomes  were  con- 
tracted and  massed  in  the  killing  and  fixation.  It  is  barely  possible 
that  this  inequality  of  mass  is  due  to  the  failure  of  the  lagging 
chromosome  to  divide,  thus  giving  an  unequal  qualitative  as  well  as 
quantitative  division  comparable  to  the  sex  chromosome ;  but  we  have 
as  yet  no  evidence  of  gamete  formation  in  this  genus.  Such  in- 
equality may  also  be  explained  by  the  passing  over  to  one  of  the 
daughter  nuclei  of  the  remnants  at  least  of  the  macrokaryosome 
(pi.  12,  figs.  48,  56).  Any  inequality  of  mass  which  is  evident  in 
early  anaphase  is  soon  obscured  by  the  growth  of  chromatin,  which 
is  proceeding  rapidly.  I  regret  that  I  have  not  found  a  sufficient 
number  of  metaphase  stages  to  warrant  a  detailed  study.  Of  the 
many  thousand  individuals  studied  I  have  seen  but  three  or  four 
equatorial  plates. 

As  suggested  above,  the  indication  of  a  peculiar  splitting  of  cer- 
tain peripheral  chromatin  granules  is  a  prophase,  not  a  metaphase 
phenomenon,  related  rather  to  the  precocious  splitting  of  the  seg- 
mented spireme.  I  have  found  no  indication  of  a  division  of  the 


1919]     Rhodes:  Binary  Fission  in  Collodidyon  triciliatum  Carter    231 

macrokaryosome  at  the  time  of  the  splitting  of  the  peripheral  granules, 
or  when  it  persists  and  is  found  on  or  near  the  equatorial  plate 
(pi.  11,  fig.  46).  As  noted  above,  it  may  (pi.  12,  fig.  48)  pass  un- 
divided to  one  of  the  poles  and  thus  to  one  of  the  daughter  nuclei 
(pi.  12,  fig.  56).  This  would  explain  the  inequality  of  the  anaphase 
ehromatin  masses.  It  may  disintegrate  (pi.  11,  fig.  43),  go  into  solu- 
tion, and  finally  enter  into  the  composition  of  the  chromosomes.  It 
may,  which  is  very  probable,  pass  from  its  niche  in  the  nuclear  mem- 
brane, out  of  the  nucleus  to  form  an  extranuclear  chromidial  cloud 
or  simply  be  dissipated  or  absorbed  into  the  cytoplasm.  It  was  found 
to  divide  into  two  unequal  segments  in  several  instances  in  the  early 
prophase  (pi.  10,  fig.  33),  but  it  is  hardly  probable  that  much  signifi- 
cance attaches  to  this,  since  it  is  not  coordinated  with  ehromatin 
divisions  elsewhere. 


ANAPHASE  AND  TELOPHASE 

After  the  transverse  splitting  and  separation  of  the  chromosomes, 
each  daughter  group  passes  toward  its  respective  pole.  When  only 
slightly  separated,  the  chromosomes  fuse  into  a  densely  staining 
mass  (pi.  12,  figs.  52,  54,  55),  but  can  hardly  be  said  to  lose  their 
identity  here,  since  knobs  and  masses  resembling  ends  of  chromo- 
somes protrude  irregularly  from  the  mass.  These  ehromatin  masses 
become  organized  into  a  skein  or  spireme,  a  great  number  of  small 
granules  arranged  on  linear  linin  threads,  before  the  nuclear  mem- 
brane has  divided  (pi.  12,  fig.  53).  The  spindle  fibers  still  persist 
(pi.  12,  fig.  52)  after  the  daughter  ehromatin  masses  have  drawn  near 
their  respective  poles,  but  are  only  slightly  visible  at  the  former 
equatorial  plate.  The  nuclear  wall  constricts  and  nuclear  division  is 
accomplished,  with  the  ehromatin  still  in  compact  masses. 

As  the  daughter  ehromatin  masses  pass  to  their  respective  poles, 
they  increase  perceptibly  in  size  until  each  equals  or  exceeds  the  size 
of  the  original  karyosome  (pi.  12,  figs.  52,  55).  This  is  evidently 
growth  and  not  concretion  or  deposition,  since  the  chromidial  cloud 
practically  disappears  at  the  metaphase  and  then  deepens  again  in 
the  anaphase. 

Toward  the  final  anaphase  the  ehromatin  mass  or  skein  breaks  up 
into  numerous  ehromatin  masses  scattered  irregularly  through  the 
daughter  nuclei.  A  cloud  seems  to  fill  the  nucleus  and  spreads  to 
the  surrounding  cytoplasm,  indicating  excessive  metabolic  activity. 


232  University  of  California  Publications  in  Zoology        [VOL.  19 

The  plane  of  division  runs  parallel  to  the  major  axis  and  the 
sulcus  or  chief  longitudinal  groove.  The  daughter  blepharoplasts 
separate  and  move  to  either  side  of  this  plane.  The  basal  granules 
divide  earlier  in  the  prophase,  as  do  probably  also  each  of  the  two 
flagella,  thus  producing  for  each  daughter  blepharoplast  two  basal 
granules  and  four  flagella.  I  find  no  stages  in  which  there  are 
shorter  or  unequal  flagella,  indicating  outgrowth  of  new  flagella,  and 
yet  no  evidence  of  splitting  has  been  observed. 

The  major  sulcus  deepens  and  in  this  plane  there  is  a  complete 
peripheral  cytoplasmic  constriction  (pi.  13,  figs.  57-60).  The  cyto- 
plasm rounds  itself  up  and  the  daughter  organisms  are  then  held 
together  by  a  thin,  highly  vacuolated,  protoplasmic  connection,  con- 
taining one  or  more  large  vacuoles.  Division  is  finally  accomplished 
by  the  rupturing  of  these  vacuoles.  At  the  time  of  final  separation, 
the  chromatin  masses  are  scattered  irregularly  through  a  clouded 
nucleus.  Part  of  these  mass  together,  round  up  into  a  karyosome  on 
which  is  deposited  the  immediately  surrounding  cloud,  thus  leaving 
a  hyaline  area.  A  large  part  of  the  chromatin  remains  on  the  out- 
side of  this  hyaline  area  and  tends  to  dissassociate,  forming  the 
peripheral  granular  area  (pi.  13,  fig.  59).  There  is  great  metabolic 
activity  at  this  stage,  for  the  whole  cell,  especially  the  anterior  end, 
is  darkened  by  a  chromidial  cloud.  At  completion  of  nuclear  re- 
organization the  rhizoplasts  assume  their  small,  almost  invisible 
appearance  and  the  typical  vegetative  organism  results. 


SUMMARY  OF  OBSERVATIONS 

1.  Verification  of  the  work  of  Carter   (1865),  Stein   (1878),  and 
France  (1899). 

2.  Failure  to  find  a  contracting  vacuole,  a  point  upon  which  pre- 
vious observers  are  at  variance. 

3.  Determination    of   a   fundamental   polarity   and   a   superficial 
symmetry,  with  anterior  and  posterior,  sulcal  and  absulcal  areas. 

4.  There  is  evidence  of  a  very  primitive  cytostome  just  at  the  base 
of  the  flagella.     The  sulcus  itself  may  be  regarded  as  an  extension 
of  the  cytostome. 

5.  The  blepharoplast  consists  of  two  basal  granules  surrounded 
by    a    granular    archoplasm.      When    not    sufficiently    destained,    it 
resembles  a  more  or  less  branched  and  attenuated  mass,  from  which 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    233 

two  tubercles  protrude.  From  each  granule  two  equal  flagella  arise. 
Two  faint  rhizoplasts  join  the  blepharoplast  to  the  nucleus  and 
karyosome.  At  the  points  of  contact  of  the  rhizoplasts  with  the 
nuclear  membrane,  very  small  granules  are  found,  which  function  as 
extranuclear  centrosomes. 

6.  The  typical  vesicular  nucleus  undergoes  a  true  mitosis  of  a 
type  probably  related  to  mesomitosis. 

7.  There  is  an  unequal  constriction  and  differential  division  of 
the    initial   karyosome,    the    resulting   karyosomes    being    designated 
macrokaryosomes  and  microkaryosomes. 

8.  A  kinetic  membrane  is  organized  around  the  microkaryosome 
and  during  the  prophase  expands  until  it  apparently  becomes  com- 
mensurate with  the  nuclear  membrane. 

9.  The  macrokaryosome  rounds  up  in  a  niche  of  the  nuclear  mem- 
brane, not  being  involved  in  mitosis.    Its  possible  fate  and  significance 
will  be  discussed  in  the  latter  part  of  this  thesis. 

10.  The  nuclear  membrane  is  persistent  during  mitosis. 

11.  There  is  evidence  for  an  extranuclear  centrosome,  such  as  has 
been  found  in  parasitic  flagellates,  but  in  this  instance  it  is  separated 
from  the  blepharoplast  and  connected  with  the  same  by  rhizoplasts. 
Further  work  on  this  and  other  free  living  flagellates  is  much  needed 
to  more  clearly  demonstrate  this  and  related  problems. 

12.  There  is  an  intranuclear  chromatin  cloud  during  the  prophase. 
In  the  final  prophase,  the  anaphase  and  telophase  an  extranuclear 
chromidial  cloud  is  also  formed. 

13.  The  microkaryosome  organizes  within  the  kinetic  membrane, 
apparently  separates  into  two  masses  connected  by  fibers  and  may 
pass  through  a  tripod  and  ring  stage.      This  passes  into  a  double 
segmented  spireme  stage,  in  which  there  are  four  terminal  chromatin 
masses  or  knobs. 

14.  A  separation  of  this  spireme  takes  place,  the  resulting  terminal 
masses,  seven  or  eight,  forming  the  chromosomes.     There  is  a  pre- 
cocious splitting  of  the  peripheral  chromatin  granules. 

15;  In  the  final  prophase  when  the  segmented  skein  is  arranged 
about  the  equatorial  plate,  there  is  a  precocious  splitting  of  the 
chromatin  masses,  which  may  be  indicative  of  the  division  and  dis- 
tribution of  the  chromosomes  which  is  about  to  take  place.  In  this 
way  the  transverse  division  of  the  chromosomes  may  be  explained  as 
a  fundamental  longitudinal  division,  as  determined  by  this  precocious 
splitting. 


234  University  of  California  Publications  in  Zoology        [VOL.  19 

16.  The  number  of  chromosomes  is  seven  or  eight,  which  in  meta- 
phase  are  arranged  on  the  equatorial  plate  of  a  perfect  spindle. 

17.  The  chromosomes  part  transversely.     In  the  only  satisfactory 
metaphase  observed  (pi.  12,  fig.  50)  one  lags  on  the  spindle. 

18.  The  resulting  chromatin  masses  in  early  anaphase  are  some- 
times unequal  in  size,  but  this  is  soon  concealed  by  a  rapid  growth  of 
chromatin  in  the  later  anaphase  and  telophase. 

19.  The  reorganization  of  a  typical  skein,  which  breaks  up  into 
chromatin  masses,  some  of  which  go  to  form  the  karyosome,  some  the 
peripheral  chromatin,  and  some  may  be  extruded. 

20.  The  basal  granules  separate,  the  flagella  split  longitudinally 
or  grow  out  anew,  the  rhizoplasts  split  from  the  nuclear  end,  and  the 
two  resulting  blepharoplasts  contain  two  new  basal  granules  from 
division  of  one  of  the  old,  inherited  from  the  old  blepharoplast,  and 
are  connected  with  four  equal  flagella  and  a  rhizoplast. 

21.  A  paradesmose  typical  of  polymastigotes  in  general  is  present 
between  the  separating  centrosomes,  on  the  nuclear  membrane. 

22.  Final  separation  of  the  cells  takes  place  in  the  plane  of  the 
sulcus,  parallel  with  the  major  axis  of  the  cell,  by  the  rupture  of  one 
or  more  of  the  vacuoles  of  the  constricted  protoplasmic  connection. 


DISCUSSION 
CLASSIFICATION  AND  RELATIONSHIP 

Prowazek  (1903&)  attempted  to  classify  the  nuclei  of  Flagellata, 
distinguishing  four  different  types,  which  Dobell  (1908)  has  summed 
up: 

1.  Simple   nuclei,   with    an    evenly    distributed   chromatic    network,    and   no 
internal  structures  (karyosome,  division  centre,  etc.),  e.g.,  Herpetomonas. 

2.  Vesicular  nuclei,  with  direct  division;   with  central  chromatin  mass  sur- 
rounded by  a  clear  zone,  across  which  a  more  or  less  distinct  network  extends 
outward  to  the  nuclear  membrane.     Such  a  nucleus  may  be  seen  in  some  species 
of  Bodo,  and  is  well  seen  in  Copromonas. 

3.  Centronuclei    containing    a    "nucleolo-centrosome"    (Keuten,    1895)    and 
separate  chromatin  masses.     This  type  of  nucleus  is  characteristic  of  Euglena 
and  its  allies.     (The  centre-nucleus,  as  denned  by  Boveri,  is  a  nucleus  which 
contains  a  cyto-centre,  either  in  a  consolidated  or  diffuse  form.     In  the  case  of 
Euglena,  etc.,  the  cyto-centre  is  the  nucleolo-centrosome,  i.e.,  is   of  the   con- 
solidated type.) 

4.  Vesicular   nuclei   with   karyokinetic   division:    e.g.,    Polytoma,    CTilamydo- 
monas,  etc. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    235 
To  these  Dobell  added  a  fifth : 

5.  Nuclei  in  which  the  achromatic  division-centre  lies  freely  in  the  cell, 
whilst  the  chromatin  is  diffuse  in  the  form  of  chromidia. 

In  such  a  classification  Collodictyon  finds  no  place.  Recent  work  of 
Tschenzoff  (1916)  on  Englena  and  of  Belar  (1916)  on  Astasia  show 
related  nuclear  phenomena  which  furnish  an  interesting  comparison 
with  Collodictyon.  These  possess  a  " nucleolo-centrosome "  (Keuten, 
1895),  the  significance  of  which  seems  not  to  be  well  understood. 
In  division  it  presents  the  appearance  of  a  centrodesmose.  Collo- 
dictyon possesses  no  such  evident  body  or  nucleolo-centrosome,  but 
there  is  evidence  of  an  extranuclear  centrosome  similar  to  that  in  other 
polymastigotes.  There  is  a  much  more  perfect  spindle  and  all 
chromatic  material  of  the  nucleus  in  the  metaphase  is  located  upon 
the  equatorial  plate.  It  thus  seems  to  have  a  more  advanced  type  of 
mitosis  than  do  the  above-mentioned  Euglenoidea.  With  the  present 
advancement  in  the  science  of  protozoology  it  would  seem  possible 
to  review  the  various  groups  of  flagellates  already  recorded,  not  only 
describing  their  typical  vegetative,  but  their  mitotic  phenomena,  and 
to  establish  complete  life  cycles  for  the  majority.  But  such  is  not 
the  ease.  All  previous  investigations  of  Collodictyon,  to  use  it  as  an 
example,  have  omitted  description  and  discussion  of  mitotic  and 
related  phenomena.  It  is  hoped  that  this  knowledge  has  been  brought 
out  in  sufficient  detail  and  accuracy  to  warrant  future  correlations 
and  comparisons,  though  little  more  than  a  beginning  is  claimed  to 
have  been  made. 

Because  of  its  plastic  nature  and  its  mode  of  incepting  food,  "for 
it  does  not  appear  to  possess  any  oral  aperture,"  Carter  (1865,  p.  289) 
classified  Collodictyon  as  a  rhizopod.  He,  however,  acknowledged  its 
similarities  to  Bodo  Ehr.,  in  its  voracity  especially,  to  Polyselmis 
viridis  Duj.,  and  to  Actinophrys  eichornii  in  its  vacuolated  cyto- 
plasm, the  "cellular  spaces  which  pervade  its  body."  These  com- 
parisons have  little  significance  today. 

Stein  (1878),  naming  it  Tetramitus  sulcatus  Stein,  placed  it  in  the 
flagellate  group  and  in  the  first  family,  Monadina,  together  with  the 
genera:  Cercomonas,  Monas,  Goniomonas,  Bodo,  Phyllomitus,  (Tetra- 
mitus}, Trepomonas,  Trichomonas.  Hexamitus,  Lophomonas,  and 
Platytheca. 

Kent  (1880-81)  interpreting  Carter's  and  Stein's  organisms  as 
different,  put  both  under  Order  IV,  Flagellata-Pantostomata ;  Collo- 
dictyon in  Family  XIV,  Trimastigidae  with  Trichomonas,  Dallingeria 


236  University  of  California  Publications  in  Zoology        [VOL.  19 

and  Trimastix;  Tetramitus  in  Family  XV,  Tetramitidae  with  Tetra- 
selmis  and  Chloraster.  He  compared  the  vacuolated  cytoplasm  to 
that  of  Noctiluca,  Leptodiscus,  Trachelius  and  Loxodes. 

Biitschli  (1883-87),  recognizing  Tetramitus  sulcatus  as  the  syn- 
onym of  Collodictyon,  characterized  it  briefly  under  the  Family 
Tetramitina  of  the  Suborder  Monadina  Biitschli,  with  Tetramitus 
Perty,  Monocercomonas  Grassi,  Trichomonas,  and  Trichomastix,  and 
placed  the  Polymastigina  as  the  succeeding  family  with  the  genera 
Hexamitus,  Megastoma,  and  Polymastix. 

France  (1899,  p.  19),  after  discoursing  on  the  inadequacy  of  the 
classification  of  flagellates,  says: 

Man  eroffnet  einfach  systematische  Kumpelkammern,  in  die  man  der 
' '  Urvater  Hausrath  drein  gestopf t. ' '  Dort  liegen  sie,  ein  triibseliges  Chaos  von 
Bodoninen,  Monadinen,  Dendromonaden,  mit  denem  man  nichts  anzufangen 
weiss.  Von  dort  holte  ich  mir  auch  meine  Collodictyon,  deren  Bau  und  Lebens- 
geschichte  darzulegen,  die  Aufgabe  der  folgenden  Zeilen  ist. 

In  concluding  his  paper  (p.  26)  he  wrote: 

Ich  begriisste  die  generische  Selbstandigkeit  mit  umsomehr  Freude,  als  ich 
der  Ansicht  bin,  Collodictyon  sie  mit  den  viel  hoher  organisierten  Tetramitiden 
gar  nich  naher  verwandt.  Es  ist  eine  sehr  primitive  Zelle,  welche  nach  Art  der 
Monadinen  gebaut  ist,  so  lebt  und  sich  sowie  sie  vermehrt.  Hohere  Differen- 
zierungen  besitzt  es  gar  nicht,  sondern  nur  lauter  solche  charaktere,  welche  es 
erfordern  diesen  Organismus  den  Monadinen  anzugliedern.  Damit  ware  aber 
mein  anfangs  gestechtes  Ziel  erreicht,  diesem  Wesen  endlich  seinen  dauernden 
Platz  im  System  anweisen  zu  kennen. 

There  is  little  agreement  among  taxonomists  since  1900  as  to  the 
group  with  which  Collodictyon  is  associated.  G.  Senn  (1900),  prob- 
ably as  consistent  as  any,  placed  it  in  the  Order  Protomastigineae 
(coordinate  with  I.  Pantostomatineae,  III.  Distomatineae,  IV.  Chryso- 
monadineae,  V.  Cryptomonadineae,  VI.  Chloromonadinae,  VII.  Euglen- 
inae),  in  the  ninth  and  last  family,  Tetramitaceae,  Avith  Costiopsis, 
Tetramitus,  (Collodictyon),  Trichomastix,  Trichomonas,  and  Poly- 
mastix. Lemmermann  (1910)  follows  Senn,  accepting  Costia  instead 
of  Costiopsis. 

Klebs  (1893)  and  Blochmann  (1895)  accept  five  orders:  Proto- 
monadina,  Polymastigina,  Euglenoidea,  Chromomonadina,  and  Phyto- 
monadina,  including  Collodictyon  in  the  Polymastigina. 

Hartmann  and  Chagas  (1910)  put  the  Protomonadina  and  the 
Polymastigina  into  a  single  order,  the  Protomonadina,  and  add  the 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    237 

orders  Rhizomastigina  and  Binucleata  (Rhizomastigina,  Protomona- 
dina,  Binucleata,  Chromomonadina,  Euglenoidea,  Phytomonadina). 
This  is  the  system  adopted  by  Hartmann. 

Calkins  (1909)  and  Lankester  (1909),  as  did  Delage  and  Herouard 
(1895),  put  Collodictyon  in  the  tribe  or  subtribe  Monostomatina, 
organisms  with  mouth  opening  at  the  base  of  the  group  of  from  four 
to  six  flagella,  as  contrasted  with  the  Astomea,  which  have  no  special 
mouth  openings.  The  sulcal  region  of  Collodictyon  may  indeed  be 
regarded  as  a  cytostome.  In  this  structure,  however,  we  have  an 
extension  of  the  cytostome  as  a  metabolic  surface.  Its  pseudopodia 
mark  it  as  a  generalized  rather  than  a  specialized  type.  Collodictyon 
may  thus  be  regarded  as  comparable  with  organisms  like  Mastig amoeba 
Schultze,  Cercomonas  crassicauda  Dujardin,  and  Tetramitus  or  Tricho- 
monas.  Regarding  the  above  classification,  therefore,  the  validity  of 
the  tribes  Astomea  and  Monostomatina  is  lessened  or  Collodictyon 
must  be  regarded  as  an  intermediate  type. 

Neither  Doflein  in  his  Lehrbuch  (1911)  nor  Minchin  in  his  Intro- 
troduction  to  Protozoology  (1912)  classify  Collodictyon.  Senn,  Klebs, 
Doflein,  and  Minchin,  however,  all  accept  the  Order  Polymastigina, 
into  which  Collodictyon  naturally  falls.  Klebs  and  Doflein  contrast 
this  with  Protomonadina,  Minchin  with  Pantastomina  and  Protomona- 
dina,  Senn  with  Pantastomatineae  and  Distomatineae.  These  distinc- 
tions by  various  authors  are  not  so  much  opposed  to  one  another  as  it 
at  first  seems.  All  accept  the  number  of  flagella  as  of  determining 
value.  It  is  very  desirable  to  have  no  all-inclusive  taxonomical  groups 
such  as  the  older  Monadina.  At  the  same  time  artificial  distinctions 
do  not  tend  to  clarify  the  situation.  Hartmann  was  evidently  actuated 
by  such  a  feeling  when  he  combined  the  Polymastigina  with  the  Pro- 
tomonadina. Collodictyon  emphasizes  the  difficulties  arising  in  estab- 
lishing the  distinctness  of  the  groups  Pantostomatina,  Protomonadina, 
Distomatineae  and  Polymastigina,  especially  when  the  nuclear 
phenomena  are  considered. 

As  to  the  location  of  the  mouth,  Collodictyon  seems  to  have  all  of 
its  body  somewhat  metabolic,  the  anterior  end  alone  being  compara- 
tively constant  in  shape,  but  the  function  of  ingesting  food  is  localized 
in  the  sulcus,  about  one-fourth  of  the  surface  of  the  organism,  assisted 
materially  by  the  posterior  part  of  the  body.  Thus,  in  this  feature, 
Collodictyon  seems  to  lie  midway  between  the  Pantostomatina  and 
the  Protomonadina  or  Polymastigina.  If  the  primitive  phylogenetic 
type  be  regarded  as  a  polarized  flagellate,  with  a  surface  entirely 


238  University  of  California  Publications  in  Zoology        [VOL.  19 

amoeboid,  then  the  sulcus  of  Collodictyon  may  be  regarded  as  a  vestigial 
character,  a  restricted  surface  area  retained  from  a  Rhizomastigina 
type.  Collodictyon  would  thus  be  closely  related  to  the  rhizopods,  not 
far  removed  from  the  ancestral  type  from  which  the  latter  diverged 
from  the  evolving  flagellates.  By  such  an  interpretation  it  would 
naturally  be  considered  an  organism  of  a  generalized  or  possibly  a 
primitive  type.  If,  however,  the  primitive  phylogenetic  type  be  re- 
garded as  a  polarized  flagellate  with  a  non-amoeboid  surface,  then  the 
sulcus  of  Collodictyon  must  be  regarded  as  a  highly  specialized  cyto- 
stome. 

Among  the  specific  and  generic  characters  of  Collodictyon  which 
may  be  called  diagnostic,  I  find : 

1.  The  number  of  flagella  is  four.    Carter  erred  in  this. 

2.  I  find  no  contracting  vacuole  (I  am  loath  to  say  that  there  is 
none).      Carter    (1865)    described  but  did   not   figure   "contracting 
vesicles;"  Kent  (1880-82,  p.  308),  with  seeming  authority  from  Carter, 
denied  that  there  were  any;  "such  an  open  vacuolar  character  of  the 
parenchyma  would  seem  to  obviate  the  necessity  for  a  contractile 
vesicle,  the  presence  of  which  structure  Mr.   Carter  was  unable  to 
detect."     Stein  (1878-83)  described  and  figured  one  in  the  anterior 
end  near  the  nucleus;  France  (1899)  with  difficulty  found  one  in  the 
anterior  end  and  timed  its  pulsation  at  about  every  forty  seconds; 
Klebs   (1893)   found  one  in  the  posterior  end  in  the  Tetramitus  he 
described  as  "sulcatus." 

3.  The  flagella  are  equal  in  length,  being  as  long  or  slightly  longer 
than  the   body.      This   possibly   was   the    basis   of   Kleb's    mistaken 
identity. 

4.  The  sulcal  region  is  a  modified  surface  area  and  may  be  regarded 
as  a  cytostome.     The  classification  of  Delage  and  Herouard   (1895), 
Lankester   (1909),  and  Calkins   (1909)   involves  this  in  their  Tribe 
Monostomatina. 

5.  There  is  an  extranuclear  centrosome  just  at  the  point  where  the 
rhizoplasts  enter  the  nuclear  membrane.     It  is,  therefore,  outside  of, 
but  connected  with,  the  blepharoplast.     In  mitosis  a  paradesmose  is 
formed  between  the  dividing  centrosomes.     These  characters  establish 
polymastigote  affinities. 

6.  Blepharoplast  (so  defined  as  not  to  include  the  division  center) 
consists  of  two  basal  granules  embedded  in  a  chromatoidal  matrix  or 
surrounded  by  a  granular  archoplasm.     The  basal  granules  are  con- 
nected to  the  nucleus  by  faint  rhizoplasts. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    239 

7.  In  mitosis  the  nuclear  membrane  is  persistent. 

8.  There  is  formed  a  perfect  spindle  of  achromatic  mantle-fibers 
with  at  least  seven,  probably  eight,  chromosomes  and  an  equatorial 
plate. 

9.  Life  cycle  so  far  discovered  is  simple,  binary  fission  by  longi- 
tudinal division  being  the  only  method  of  reproduction  known. 

Collodictyon  is  typically  an  animal  of  simple  organization.  Its 
phylogenetic  stem  grows  out  of  the  unknown  past.  It  is  very  close 
to  the  stem  from  which  the  Rhizopoda  and  Mastigophora  branch, 
having  much  in  common  with  each.  That  Collodictyon  is  one  of  the 
simplest  and  most  primitive  of  the  Polymastigina,  there  can  be  no 
doubt.  With  the  free  living  members  of  the  genus  Tetramitus  (not 
accepting  T.  ckilomonas  as  such)  it  finds  its  nearest  relatives.  Costia, 
Tetramitus  (saprophytic  and  parasitic),  Trichomastix,  Polymastix, 
and  Trichomonas  are  derivatives  of  either  the  Collodictyon  type  or 
free  living  Tetramitus.  Thus  knowing  possibly  the  simplest  Tetra- 
mitidae,  I  am  prone  to  regard  this  group  as  not  so  complex  in  its 
entirety  as  France  (1899)  would  have  us  believe  when  he  wished 
Collodictyon  related  to  the  Monadaceae  rather  than  the  "complex 
Tetramitaceae. "  Much  of  this  complexity  may  be  interpreted  as  the 
result  of  morphological  changes  resulting  directly  or  indirectly  from 
parasitism. 

In  Collodictyon  the  two  basal  granules  with  very  faint  rhizoplasts 
connected  with  the  microkaryosome  are  not  necessarily  so  highly  differ- 
entiated, when  it  may  be  regarded  as  simply  a  slight  advance  over 
Cercomonas  (Wenyon,  1910,  text  fig.  18),  due  to  the  multiplication  of 
flagella,  or  a  doubling  of  the  flagella  of  a  biflagellate  type.  Collodictyon 
is  a  primitive  polymastigote. 

PARASITISM  AND  SYMBIOSIS 

For  some  three  months,  January  to  March,  1916,  the  majority  of 
all  individuals  of  Collodictyon  were  filled  with  algae,  which  were 
identified  as  Chlorella  vulgaris.  Only  at  the  period  of  longitudinal 
division  and  in  moribund  stages  would  they  become  free  from  these 
inclusions.  The  algae  were  arranged  peripherally,  just  beneath  the 
surface  and  it  looked  at  times  as  though  Collodictyon  were  hollow. 
Often  when  under  observation  these  algae  could  be  seen  to  form  small 
nodules  and  pop  out  of  the  pellicle.  These  were  seldom  surrounded  by 
a  hyaline  area  indicating  that  they  were  being  used  for  food,  though 
at  periods  nearly  all  were  so  absorbed. 


240  University  of  California  Publications  in  Zoology        [VOL.  19 

From  the  above  similar  and  repeated  observations  I  was  forced  to 
conclude  that  we  haveJhere  a  case  of  parasitism  or  possible  symbiosis. 
Such  a  Collodictyon  seldom  engulfed  food  and  seemed  well  nourished, 
as  though  by  holophytic  nutrition.  For  some  months,  in  spite  of  daily 
observations,  I  never  observed  pseudopodia  protruded  from  the  sulcal 
region  in  such  individuals,  which  condition  is  characteristic  of  the 
holozoic  phase.  If  such  be  regarded  as  parasitism,  Collodictyon  must 
be  regarded  as  the  parasite,  and  Cklorella  must  provide  the  nourish- 
ment. Possibly  it  had  best  be  regarded  as  a  case  of  benign  domestica- 
tion, the  by-products  alone  being  used.  To  be  truly  a  symbiotic  relation- 
ship, Chlorella  would  have  to  be  benefited,  and  I  have  not  been  able 
to  determine  that  this  was  the  case.  I  do  know  that  it  thrived  fully  as 
well,  if  not  better,  outside  the  organism. 

The  question  of  inclusions  functioning  in  a  parasitic  or  symbiotic 
relation,  is  not  a  new  one.  The  "yellow  cells"  of  Radiolaria  is  one  of 
the  most  interesting  as  well  as  most  disputed  points,  and  one  which  is 
still  far  from  being  satisfactorily  solved.  They  were  first  described 
by  Huxley  in  Thalassicolla,  and  verified  by  Johannes  Miiller  and 
Haeckel.  Cienkowski  (1871)  strongly  contended  that  they  were  para- 
sitic algae.  The  discussion  progressed  with  Richard  Hertwig  (1898, 
1902),  K.  Brandt  (1881,  1882,  1885),  Entz  (1882),  and  F.  Keeble 
(1909),  adhering  with  certain  reservations  or  modifications  to  Cien- 
kowski's  interpretation.  Miiller  had  at  first  indicated  the  possibility 
that  they  were  phases  in  the  life  cycle,  but  later  gave  up  this  concep- 
tion. In  1909  Moroff  and  Stiasny  contended  that  the  yellow  cells  of 
Acanthrometron  pellucidum  were  part  of  the  developmental  cycle ;  in 
1910  Stiasny  extended  this  interpretation  to  Sphaerozoa  and  Radio- 
laria generally.  Such  a  view  was  not  accepted  without  reservation  by 
Minchin  (1912)  ;  so  the  question  stands,  awaiting  further  and  decisive 
evidence. 

In  Collodictyon,  there  can  be  no  doubt  that  the  inclusions  are  algae. 
They  correspond  with  the  free  Chlorella  of  the  aquarium.  I  did  at 
first  mistake  them  in  observations  upon  unstained  material  to  be  ele- 
ments of  multiple  fission,  but  was  forced  to  give  this  up  upon  critical 
examination.  Neither  can  it  be  a  situation  similar  to  Euglena  gracilis 
(Zumstein,  1899),  in  which  the  typical  chloroplast  is  lost  and  an 
Astasia-like  phase  results;  though  such  evidence  furnishes  a  most 
interesting  possible  analogy.  That  an  ultimate  lichenoid  condition 
might  result  is  a  possibility  and  from  such  a  relation  Collodictyon 
might  be  transformed  from  a  holozoic  to  an  independent  holophytic 
state. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    241 

The  possibility  of  Collodictyon  becoming  ectoparasitic  upon  the 
gills  or  endoparasitic  in  the  intestine  is  a  very  fertile  field  for  specula- 
lation  and  experiment.  I  have  nearly  always  found  Collodictyon  when 
examining  preparations  brushed  from  the  gills  of  goldfish  of  the 
aquarium.  This  may  have  been  due  to  their  normal  abundance  in  the 
water.  In  attacking  dinoflagellat.es,  large  Euglena,  and  other  rapid, 
free-swimming  organisms,  Collodictyon  may  grasp  the  body  of  its 
prey  in  a  death  clasp  \vith  all  four  flagella.  At  times  I  have  seen  one 
flagellum  free  in  such  attacks.  Normally,  in  attaching  itself  to  the 
substrate  all  four  flagella  are  spread  out  radially  and  its  body  may 
be  drawn  down  close  and  tight  or  left  suspended  at  a  considerable 
height.  In  such  a  state  it  can  revolve  clockwise  or  counter-clockwise 
upon  its  major  axis.  We  can  hardly  imagine  Collodictyon  modified 
directly  into  a  Costia-like  animal,  though  the  differences  are  not  so 
great.  In  Costia  there  are  four  flagella,  two  of  which  are  long  and 
used  for  fixation,  two  of  which  are  short  and  used  for  wafting  food 
to  the  cytostome.  All  four  function  in  locomotion.  In  Collodictyon, 
the  four  flagella  occur  in  two  pairs  with  separate  basal  granules,  but 
all  are  of  equal  length  and  undifferentiated  in  structure  and  function. 
When  we  consider  its  omnivorous  propensities  it  seems  possible  that 
it  could  easily  adapt  itself  to  an  ectoparasitic  life,  and  possibly  does  so. 

Its  extreme  delicacy  of  protoplasmic  texture  and  tendency  to 
rupture  under  slightly  unfavorable  conditions,  makes  it  improbable 
that  it  may  directly  become  an  endoparasite,  even  in  the  rectal  region 
of  fishes.  That  it  could  not  pass  uninjured  through  the  stomach  and 
into  the  intestine,  would  be  evident  to  all  who  could  observe  it  closely. 
But  its  great  variation  in  size  with  correlated  reduction  of  cytoplasmic 
vacuoles,  and  the  possible  modification  of  the  sulcal  region  into  a 
cytostome  similar  to  that  in  Trichomonas,  or  a  cytostomal  region  of 
attachment,  leads  me  to  offer  Collodictyon  as  a  possible  free-living 
ancestral  type,  or  near  relative  of  such  at  least,  of  these  highly 
specialized  genera. 

MITOSIS 

Since  the  discovery  of  a  method  of  cell  division  by  Remak,  the 
evidence  of  mitotic  phenomena  has  accumulated  rapidly.  The  early 
discussion,  and  late  as  well,  centers  about  the  universality  and  then 
the  very  existence  of  amitosis  as  a  method  of  cell  or  nuclear  division. 
To  this  mooted  question  my  observations  can  add  but  little  of  decisive 
value.  It  is  evident  that  Collodictyon  presents  still  another  example, 


242  University  of  California  Publications  in  Zoology        [VOL.  19 

among  flagellates,  of  mitosis.  There  is  not  sufficient  evidence  yet  to 
generalize,  but  there  is  a  probability,  previously  expressed  by  many, 
that  with  a  fuller  knowledge  of  flagellates,  amitosis  as  a  normal 
method  of  cell  division  in  Protozoa  will  be  reduced  to  a  minimum. 
All  work  on  flagellates  and  rhizopods  in  which  amitosis  has  been 
recorded,  should  be  reworked  carefully  and  patiently,  for  the  meta- 
phase  spindle  is  not  a  structure  of  long  duration,  very  few  instances 
being  met  with  in  the  vast  number  of  vegetative  and  karyokinetic 
individuals,  and  the  various  stages  and  figures  of  the  prophase  are 
readily  capable  of  erroneous  interpretation. 

There  are  several  important  problems  related  to  the  differential 
division  of  the  karyosome.  In  the  first  place  it  in  no  way  involves  the 
question  of  amitosis  as  a  type  of  reproduction. 

That  there  is  here  any  phenomenon  of  chromatin  reduction,  homolo- 
gous to  maturation,  must  be  regarded  with  equal  skepticism.  The 
phenomena  of  sex  have  been  established  for  the  Phytomonadina  for 
years  (Dobell,  1908).  The  nuclear  details  of  the  sexual  process  in  this 
group  are  still  hard  to  explain.  In  other  flagellates  sex  phenomena 
have  received  little  confirmation.  Maturation,  such  as  is  regarded  as 
necessary  in  sexual  reproduction  among  higher  plants  and  animals, 
has  had  little  corroborative  evidence  among  flagellates.  Dobell  (1908) 
worked  out  the  life  cycle  of  Copromonas  subtilis  and  figures  nuclear 
extrusion  of  chromatin  in  the  form  of  two  polar  bodies.  These  are 
not  described  as  the  products  of  mitosis,  however.  On  critical  exami- 
nation Dobell 's  work  is  not  convincing.  His  evidence  is  inadequate 
and  thus  far  has  not  been  verified.  Goldschmidt  (1907)  described 
similar  phenomena  for  Mastigella  vitrea.  His  observations  are  less 
satisfactory  than  Dobell 's.  Schaudinn  (1904)  in  error  extended  the 
sexual  process  to  Trypanosoma  noctuae. 

Nuclear  extrusion  of  chromatin  is,  however,  a  common  phemonenon 
in  flagellates  and  protozoa  generally.  Work  on  Trichomonas  (Kofoid 
and  Swezy,  1915)  reveals  chromatin  extrusion  in  each  of  these  forms. 
Among  Amoeba  of  the  Umax  group  (Alexeieff,  19116,  1912&,  1912&), 
a  similar  extrusion  occurs.  But  all  of  these  extrusions  as  described, 
with  the  exception  of  Copromonas,  seem  to  have  no  relation  to  matura- 
tion phenomena. 

Collodictyon  (pi.  10,  figs.  29-36)  presents  a  clear  case  of  separation 
of  chromatin  from  that  which  organizes  for  mitosis  in  the  differential 
division  of  the  karyosome  (pi.  10,  fig.  32).  In  one  instance  the 
macrokaryosome  is  seen  in  a  state  of  division  (pi.  10,  fig.  33)  very 


!919]     Rhodes :  Binary-  Fission  in  Collodictyon  triciliatum  Carter    243 

comparable  to  the  division  of  a  polar  body,  but  there  is  no  adequate 
basis  for  any  maturation  process.  Another  phase  (pi.  13,  fig.  60) 
was  found  in  which  there  are  two  nuclei  in  a  partially  constricted 
individual.  This  may  be  a  late  telophase,  but  in  each  nucleus 
can  be  seen  a  small  chromatic  body  near  the  central  karyosome. 
Furthermore  there  is  a  food  vacuole  containing  a  recently  engulfed 
Pandorina.  This  is  contrary  to  the  rule.  At  the  beginning  of 
mitosis  all  food  particles  are  extruded  and  this  is  the  only  instance 
in  which  it  seems  food  has  been  engulfed  before  karyokinesis  is  com- 
pleted. It  is  interesting,  therefore,  to  contemplate  the  possibilities. 
It  may  be  interpreted  as  follows :  1.  A  telophase  phenomenon,  present- 
ing the  anomalies  of  the  small  chromatic  mass  near  the  karyosome  of 
unknown  function,  but  probably  metabolic,  and  the  engulfed  Pan- 
dorina. 2.  A  somatella  of  two  cells  or  a  suspended  telophase  which 
has  actively  begun  to  engulf  food.  3.  Conjugating  individuals  in 
which  polar  bodies  are  being  extruded.  Since  conjugation  has  never 
been  observed  in  living  material  and  this  is  the  only  instance  capable 
of  such  an  interpretation,  it  seems  improbable.  The  first  alternative 
leaves  much  to  be  desired,  since  it  gives  no  explanation  of  the  excep- 
tional phenomenon.  This  leaves  the  interpretation  of  a  suspended 
telophase  or  a  two-celled  somatella  as  the  most  probable  explanation. 
It  can  not  be  considered  of  much  critical  value  until  further  verified 
and  elucidated.  "We  may,  however,  at  least  exclude  the  probability  of 
maturation  phenomena.  In  Collodictyon  is  found  a  beautiful  illustra- 
tion of  the  separation  of  excessive  chromatin  from  the  mass  undergoing 
mitosis,  thus  freeing  that  body  for  its  generative  function.  It  presents 
little  probability  of  sexual  phenomena.  If  I  may  be  allowed  to  sur- 
mise, acknowledging  how  illogical  such  a  surmise  is,  all  such  matura- 
tion phenomena,  recorded  in  the  Flagellata,  may  be  nothing  more  than 
the  amitotic  division  of  the  karyosome,  as  is  evident  in  Collodictyon, 
a  freeing  of  the  nucleus  of  excessive  or  surplus  chromatin. 

The  surface-volume  ratio  hypothesis  is  not  supported  by  the  cell 
division  of  Collodictyon,  since  all  sizes  of  cells  are  found  undergoing 
division  (pi.  11,  figs.  40,  45,  pi.  12,  figs.  47,  51,  54).  There  is  an 
apparent  indifference  to  size. 

The  theory  of  nucleao-cytoplasmic  ratio  is  much  more  difficult  to 
prove  or  disprove  positively.  Collodictyon  presents  a  double  line  of 
evidence :  First,  the  differential  division  of  the  karyosome  may  be 
interpreted  as  either  (a)  a  method  of  chromatin  extrusion,  such  as  has 
repeatedly  been  recorded  for  many,  the  majority  of  the  Plasmodro- 


244  University  of  California  Publications  in  Zoology        [VOL.  19 

mata;  (&)  simply  the  freeing  of  the  karyosome  of  sufficient  chromatin, 
which  may  here  be  regarded  as  passive  and  inert,  to  permit  of  un- 
retarded  kinetic  activity  on  the  part  of  the  generative  microkaryosome, 
or  (c)  both.  The  second  line  of  evidence  points  toward  a  separation 
of  the  chromatin  preliminary  to  a  reorganization  and  growth  of  the 
same.  It  is  necessary  for  the  peripheral  chromatin  as  well  as  that 
in  the  macrokaryosome  to  pass  through  solution,  usually  through  the 
stage  of  a  chromidial  cloud  as  well,  before  entering  into  the  prophase 
skein  and  the  metaphase  chromosomes  whose  organization  takes  place 
within  the  metabolic  membrane.  The  chromatin  upon  the  equatorial 
plate  is  much  greater  in  amount  than  the  mass  of  the  original  micro- 
karyosome. Growth  and  organization  have,  therefore,  definitely  taken 
place.  Subsequently,  growth  proceeds  much  more  rapidly  in  the 
anaphase,  during  which  time  each  daughter  nucleus  comes  to  contain 
almost  if  not  fully  as  much  chromatin  as  the  original  nucleus  (pi.  12, 
figs.  52-55).  This  would  indicate  that  cell  division  was  not  initiated 
by  an  unbalanced  ratio  and  that  the  chromatin-cytoplasmic  equilibrium 
may  be  simply  a  metabolic  phenomenon,  not  at  all  related  to  initiating 
cell  division.  It  would  point,  however,  to  the  necessity  of  freeing  the 
microkaryosome  to  insure  its  better  kinetic  activity  and  that  a  dividing 
nucleus  seeks  to  be  unretarded  by  surplus  chromatin  when  organizing 
for  division.  Collodictyon  thus  presents  evidence  which  tends  to 
contradict  the  nucleo-cytoplasmic  ratio  theory. 

The  problem  of  dual  chromatin  is  especially  inviting.  There  are 
two  types  of  chromatin  in  Collodictyon,  differing  clearly  and  unmis- 
takably in  behavior.  Repeated  efforts  to  get  a  differential  stain  for 
the  macrokaryosome  and  microkaryosome,  however,  have  not  succeeded, 
and  we  have  no  evidence  whatever  of  any  chemical  or  physical  differ- 
ence between  the  chromatin  of  these  structures.  Observations  upon 
the  microkaryosome  lead  me  to  interpret  that  body  as  consisting  of  the 
generative  chromatin.  In  its  function  at  least,  this  chromatin  is 
different  from  that  of  the  separated  macrokaryosome,  which  is  both 
physiologically  and  morphologically  passive.  It  required  little  specu- 
lation to  conceive,  in  fact  it  is  perhaps  probable,  that  with  differentia- 
tion in  functioning,  the  chemical  nature  of  the  chromatin  might  be 
sufficiently  altered  by  purely  metabolic  changes  to  produce  differential 
staining  of  the  two  bodies.  That  such  a  differential  staining  has  not 
been  achieved,  points  emphatically  to  the  fundamental  similarity  and 
chemical  nature  of  all  the  chromatin  of  Collodictyon.  Collodictyon 
seems  to  present  an  example  among  flagellates  of  trophochromatin  and 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    245 

idiochromatin.     Such  a  distinction  in  this  instance  is,  however,  more 
physiological  than  morphological. 

Conceived  in  such  a  category,  Collodictyon  may  stand  closely 
related  to  the  parasitic  flagellates  containing  a  parabasal  body  (kineto- 
nucleus  of  Hartmann).  This  would  emphasize  the  fact  that  Hart- 
mann  's  Binucleata  is  based  upon  a  fundamentally  physiological  rather 
than  a  true  morphological  character.  The  macrokaryosome,  through 
the  changing  metabolic  equilibrium,  brought  about  by  change  from  a 
free  living  to  a  parasitic  mode  of  life,  might  be  preserved  and  persist 
as  a  result  of  purely  chemical  reaction,  thus  becoming  the  parabasal 
body.  This  possible  origin  of  the  parabasal  body  is  purely  theoretical. 
Rhynochonionas  (Belar,  1916)  and  Bodo  caudatus  (Alexeieff,  1911a), 
as  far  as  I  know,  are  the  only  free  living  flagellates  having  any  per- 
sistent character  comparable  to  a  parabasal  body.  The  fact  that  the 
parabasal  body  is  not  present  in  all  parasitic  flagellates,  nor  constant 
in  the  life-history  of  some,  would  emphasize  its  dependence  upon 
chemical  nucleo-cytoplasmic  equilibrium  and  its  probable  origin  from 
a  primitive  condition  such  as  is  found  in  Collodictyon. 

Werbitsky's  work  (1910),  in  which,  by  feeding  host  rats  para- 
fuchsin,  tryparosin  or  oxazine,  the  parabasal  body  was  dissolved  and  a 
strain  of  parasites  obtained  in  which  this  body  did  not  appear  through 
several  successive  generations,  may  be  similarly  interpreted.  Anything 
tending  to  counterbalance  or  upset  the  metabolic  equilibrium  of  the 
cell  would  be  expected  so  to  affect  a  simple  passive  mass  of  chromatin 
which  no  longer  functions  in  its  original  role,  but  persists  as  a  surplus 
or  reserve.  Since  chromatin  seems  to  be  the  substance  in  which  meta- 
bolism centers,  the  parabasal  body  would  thus  probably  function  as  a 
kinetic  reservoir  for  the  motor  activities  of  the  cell.  Evidence  from 
Collodictyon  emphasizes  this  interpretation  of  Kofoid  and  Swezy 
(1915). 

Mitosis  in  Metazoa  is  variable  in  its  details,  but  as  found  in  the 
Protozoa  it  is  variable  in  its  fundamental  features,  so  much  so  that 
it  may  be  classified  into  categories.  Little  distinction  was  made  in  the 
types  of  mitosis  until  Nagler  (1909,  p.  46)  designated  what  had  pre- 
viously been  called  amitosis  in  Amoeba  and  many  Protozoa  as  "pro- 
mitosis"  in  contrast  to  the  type  of  mitosis  as  found  in  Metazoa  and 
Metaphyta.  "Fur  die  sogannte  Amitose  der  Protozoen  fuhrt  man 
daher  am  besten  eine  neue  Bezeichnung  ein  und  definiert  sie  als  eine 
Kernteilung,  die  weder  ausgesprochene  Mitose,  noch  Amitose  ist  und 
sich  charakterisiert  durch  die  Teilung  eines  Nucleocentrosoms,  des 
Caryosoms.  Ich  schlage  deshalb  fur  diese  Teilungsform  den  Namen 


246  University  of  California  Publications  in  Zoology        [VOL.  19 

Promitose  vor. "  Flemming  (1882)  suggested  the  terms,  "amitosis" 
and  "mitosis,"  and  defined  the  former  as  a  nuclear  division  without 
formation  of  chromosomes  and  a  spindle,  while  in  mitosis  these  are 
more  or  less  evident.  Nagler  (1909,  p.  46)  thinks  amitosis  would  be 
better  characterized  "durch  die  unregelmassige  Durchschniirung  des 
Kernes  (Fragmentierung)."  He  concludes  that  an  extreme  instance 
of  amitosis  is  not  known  in  the  Protozoa,  instances  so  interpreted,  with 
division  of  centriole  within  the  karyosome  and  the  apparent  division  of 
the  whole  chromatin  mass,  being  more  analogous  to  mitosis  than  amitosis. 
Chatton  (1910)  distinguished  three  types  of  mitosis,  which,  as  he 
characterized  them,  may  be  analyzed  as  follows  : 

Promitosis. — (Protokaryon  type  of  nucleus,  consisting  of  a  fundamental 
mass  of  plastin,  impregnated  with  chromatin,  and  containing  a  centriole). 

1.  Nuclear  membrane  is  persistent  and  division  is  intranuclear. 

2.  Karyosome  is  the  equivalent,  morphologically  and  physiologically  of  the 
centrosome. 

3.  Equatorial   plate    (chromosomes?)    organized    from   peripheral   chromatin 
material. 

4.  Chromatin  is  not  distributed  equally  by  the  nuclear  mechanism. 

5.  Achromatic  separation  fibers  are  apparent  when  the  karyosome  divides. 

Thus  all  essential  elements  and  the  primitive  substances,  except 
peripheral  chromatin  (wrhich  may  be  most  important),  are  condensed 
within  the  karyosome.  In  higher  forms  of  mitosis  these  tend  to 
separate.  "In  proportion  as  the  karyosome  loses  its  plastin  and 
chromatin  elements,  and  becomes  reduced  to  the  centriole  alone,  so  the 
primitive  promitosis  will  approach  more  and  more  to  the  type  of  an 
ordinary  mitosis"  (Minchin,  1912,  p.  110).  This  reduction  of  the  karyo- 
some may  be  either  temporary,  taking  place  only  during  the  process  of 
mitosis,  or  permanent,  as  is  characteristic  of  higher  types  of  mitosis. 

Mesomitosis. — 

1.  Nuclear  membrane  persistent  and  division  intranuclear. 

2.  Centriole,  more  or  less  separated  from  the  karyosome,  rests  within  the 
nucleus. 

3.  Chromosomes  derived  from  the  karyosome. 

4.  Chromosomes  (equatorial  plate)  organized  upon  a  spindle. 

5.  Plastin  is  reduced  or  disappears. 
Metamitosis. — 

1.  Nuclear  membrane  disappears  during  process  of  mitosis,  the  mitotic  figure 
resting  in  the  cytoplasm. 

2.  Centriole,    separate    from    the    karyosome,    may   be    intranuclear    (as    in 
Pelomyxa),  but  is  generally  extranuclear. 

3.  Evident  chromosomes  splitting  longitudinally  upon  an  equatorial  plate. 

4.  With   the   zones   of    differentiated,   surrounding   cytoplasm    the    centriole 
forms  the  centrosome.     Polar  asters  are  usually  present. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    247 

Chatton  thus  emphasized  or  summarized  three  categories : 

1.  Division    center    within    the    karyosome    (nuclear    membrane    persistent, 
chromosomes  organized  from  peripheral  chromatin). 

2.  Division  center  outside  the  karyosome,  but  within  the  nucleus    (nuclear 
membrane  persistent,  the  karyosome  organizing  the  equatorial  plate). 

3.  Division  center  extranuclear  (nuclear  membrane  disappears,  chromosomes 
organized  from  nuclear  chromatin). 

Collodictyon  falls  into  none  of  these  categories.  This  system  is 
based  upon  Amoeba  and  can  not  be  extended  without  modification  to 
include  the  typical  polymastigote  type  of  mitosis,  in  which  the  nuclear 
membrane  is  persistent  and  the  division  center  extranuclear.  Analysis 
of  the  mitotic  phenomena  of  Collodictyon  may  be  correlated  and 
summarized  here. 

1.  The  unequal  constriction  or  differential  division  of  the  karyo- 
some into  microkaryosomes  and  macrokaryosomes,  which  differ  at  least 
in  behavior.    The  microkaryosome  organizes  directly  into  the  segment- 
ing skein.     The  macrokaryosome  is:   (a)   extruded  from  the  nucleus 
and  absorbed  into  the  cytoplasm,  producing  an  extranuclear  chromidial 
cloud ;  or  ( 1) )  distributed  as  a  unit  to  one  of  the  daughter  nuclei ;  or 
(c)  is  absorbed  in  the  intranuclear  cloud  and  probably  is  involved  in 
chromosome  organization.     These  two  derivatives  seem  to  offer  good 
examples  of  so-called  trophochromatin  and  idiochromatin. 

2.  The    presence    of   an    extranuclear    centrosome.      Intranuclear 
chromatin  cloud. 

3.  The  presence  of  a  paradesmose. 

4.  Nuclear  membrane  persistent. 

5.  Successive  separation  of  promitotic  segmented  skein.    Indication 
of  a  precocious  splitting  of  the  peripheral  chromatin  granules  of  the 
nucleus.     Evident  precocious  splitting  of  final  segmented  skein  in 
prophase. 

6.  A   well   defined  intranuclear   spindle    (of   mantle-fibers).     No 
extranuclear  astral  rays. 

7.  Definite  chromosomes,  organized  upon  equatorial  plate,  probably 
derived  from  chromatin  of  the  microkaryosome  and  the  intranuclear 
chromatin  cloud  formed  by  the  going  into  solution  of  the  peripheral 
chromatin  granules  and  probably  the  macrokaryosome. 

8.  Apparent  transverse  splitting  of  the  chromosome  in  metaphase. 
That  it  is  impossible  to  use  Chatton 's  categories,  unmodified,  will 

inevitably  be  concluded  from  only  a  slight  survey  of  protozoan  mitosis. 
If  emphasis  be  laid  upon  the  division-center,  accepting  this  as  the 


248  University  of  California  Publications  in  Zoology        [VOL.  19 

homologue  of  centriole,  Binnenkorper  and  centrosome,  and  other  char- 
acters be  excluded,  then  the  classification  may  be  all-inclusive.  But 
whenever  other  characters  are  correlated,  exceptions  or  connecting 
links  become  as  common  or  more  so  than  the  rule,  and  only  arbitrary 
progress  is  made. 

Alexeieff 's  ' ' Systematization  de  la  mitose  dite  'primitive,'  "  (1913) 
into  five  types — promitose,  haplomitose,  mesomitose,  paramitose,  and 
panmitose — each  subdivided  into  two  subtypes,  is  the  best  possible 
illustration  to  what  extremes  one  will  be  led  who  attempts  to  bring  order 
out  of  the  chaos  of  protozoan  mitoses.  With  this  elaborate  schedule, 
there  are  many  misfits  and  the  exceptions  become  the  rule  or  the  logical 
connecting  links.  Euglena  (Tschenzoff,  1916)  fits  into  none  of  the 
categories.  Collodictyon  fails  to  conform  to  any  of  his  categories,  -the 
centrosome  being  extranuclear  and  the  nuclear  membrane  persistent. 
Furthermore,  the  chromosomes  form  partly  from  the  chromatin  of  the 
microkarosome,  partly  it  seems  from  the  macrokaryosome  and  partly 
from  peripheral  chromatin  granules,  just  as  in  panmitose.  Thus  it, 
too,  is  a  conspicuous  exception  and  emphasizes  the  arbitrariness  of 
such  attempts  at  elaborate  classification. 

Alexeieff  (1913)  attached  little  importance  to  the  presence  or 
absence  of  an  equatorial  plate,  as  a  basis  for  classifying  mitoses.  His 
reasons  assigned  are  very  good  and  can  be  referred  to  by  all  interested. 
He  emphasized  the  "centriole  theory"  and  distinguished  three  types 
of  mitotic  figures  as  they  possess  (1)  polar  bodies,  (2)  centrioles,  or 
(3)  neither  polar  bodies  nor  centrioles.  He  suggested  that  polar  bodies, 
reduced,  might  be  homologous  to  centrioles,  but  then,  with  fine-spun 
distinctions,  claimed  that  such  were  only  present  in  mesomitosis  and 
rheomitosis.  What  he  regarded  as  the  "pseudo-polar  bodies"  of 
haplomitosis,  not  being  siderophile,  could  not  be  homologized  with 
centrosomes  by  him;  he,  therefore,  concluded  that  haplomitosis  was 
very  primitive  and  ' ' particuliere. "  Hartmann  (1911),  Nagler  (1909), 
and  Chatton  (1910)  considered  centrioles  very  general  in  Protozoan 
nuclei;  Dangeard  (1901),  Alexeieff  (1913),  and  Glaser  (1912)  con- 
sidered them  very  rare. 

Calkins  (1903)  suggested  the  constitution  and  role  which  chromatin 
plays  in  division  as  a  basis  for  classification  of  the  types  of  mitosis. 
Tschenzoff  (1916)  expressed  the  same  suggestion,  having  failed  to  find 
a  division  center  in  Euglena,  except  the  nucleolo-centrosome,  the 
Binnenkorper  not  initiating  cell  division,  but  persisting  much  as  a 
nucleolus  of  metozoa. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    249 

Chatton  (1910)  attached  much  importance  to  the  absence,  per- 
sistence, or  disappearance  of  the  nuclear  membrane.  Alexeieff 
(1913,  p.  357)  said,  "Je  ne  puis  pas  portager  1'opinion  que  la  per- 
sistance  ou  la  disparition  de  la  membrane  nucleaire  a  quelque  im- 
portance." After  citing  C entropy xis  aculeata,  Octomitus  intestinalis, 
where  the  nuclear  membrane  persists  through  all  phases  of  mitosis, 
and  Hexamitus  intestinalis  in  which  the  nuclear  membrane  disappears, 
Alexeieff  (1908)  concluded:  "En  effet  dans  beaucoup  de  cas  il  est  tres 
malaise  de  decider  si  la  membrane  nucleaire  a  disparu  complement, 
ou  si  elle  est  seulement  amincie;  souvent  il  n'y  a  q'une  separation 
physique  entre  le  cytoplasme  et  le  sue  nucleaire  (comme  entre  deux 
liquides  immiscibles)  et  1 'image  cytologique  peut  etre  dans  ce  cas 
difficile  a  interpreter." 

Calkins  in  1898  and  in  later  works  describes  Tetramitus  chilomonas 
as  an  example  of  a  non-nucleated  flagellate  or  rather  of  a  distributed 
nucleus.  He  likewise  (1899)  considered  Chilomonos  paramoecium  to 
have  no  nuclear  membrane.  Kepner  and  Edwards  (1916)  prove 
this  latter  to  be  incorrect.  I  came  to  the  same  conclusion  from 
observations  of  material  put  up  in  1916.  I  am,  therefore,  skeptical 
of  the  accuracy  of  Calkin's  description  of  Tetramitus  chilomonas. 
This  form,  so  far  as  I  can  judge,  is  not  a  true  Tetramitus  but  of  a 
typical  Chilomonas  structure.  The  granules  of  the  cell  may  or  may 
not  be  chromidia.  Distributed  granules  of  some  character  (idio- 
chromatin  or  paramylum)  are  characteristic  of  the  genus  Chilomonas, 
The  division  center  would  thus  be  considered  either  within  the  nucleus 
or  the  karyosome.  It  needs  correction,  verification,  or  elucidation. 

The  nature  of  the  division  center  in  flagellates  is  not  well  under- 
stood. Prowazek  (1903)  classifies  flagellates  with  regard  to  this  division 
center  and  his  work  was  accepted  with  slight  additions  by  Dobell 
(1908).  Chatton  (1910)  classified  primitive  mitoses  in  Amoeba,  basing 
his  system  upon  the  relationship  of  the  division  center  to  the  nucleus 
and  karyosome.  Alexeieff  (1913)  gave  a  most  elaborate  system  of  the 
primitive  mitoses,  so  elaborate,  in  fact,  that  it  is  of  little  service.  Most 
references  in  recent  years  have  reverted  to  the  simpler  system  of 
Chatton  (1910).  In  all  of  these  the  relationship  of  the  division  center 
to  the  nuclear  chromatin  has  been  accepted  as  the  basis  of  differen- 
tiation. Calkins  (1903)  based  his  system  upon  the  behavior  of  the 
chromatin.  He  (1899),  however,  based  his  conception  of  the  evolution 
of  metazoan  mitoses  upon  the  extranuclear  division  center  of  Noctiluca. 


250  University  of  California  Publications  in  Zoology        [VOL.  19 

Hartmann  (1910)  in  his  new  group  Binucleata  adopted  the  con- 
ception of  an  extranuclear  division  center  located  in  the  blepharoplast. 
This  seems  to  hold  good  for  many  polymastigotes.  There  is  always 
present  a  paradesmose,  which  is  probably  comparable  to  the  centrodes- 
mose  of  rhizopods  or  the  "Binnenkorper"  of  free-living  flagellates. 


KINETIC  MEMBRANE 

The  phenomenon  of  a  membrane  organizing  around  the  micro- 
karyosome,  commensurate  with  the  inner  boundary  of  the  hyaline 
area,  and  expanding  progressively  during  the  prophase  until  it 
approaches  and  becomes  identified,  identical  except  for  the  part  where 
the  macrokaryosome  rests,  with  the  nuclear  membrane,  as  is  found  in 
Collodictyon,  so  far  as  I  know,  has  been  recorded  in  no  other  instance. 
Achromatic  radiations  from  the  karyosome  through  the  surrounding 
hyaline  area  are  found  in  the  nuclei  of  some  amoebas  (usually  de- 
scribed as  characteristic  of  protokaryon  type  of  nucleus).  These  have 
been  interpreted  as  being  related  more  or  less  closely  to  chromosome 
formation.  Sutton  (1900)  discovered  what  he  designated  "chromo- 
some vesicles, ' '  surrounding  the  organizing  chromosomes  in  an  orthop- 
teran  insect.  Carothers  (1915)  finds  the  same  in  the  nuclei  of  Culex 
and  modifies  the  term  to  "chromomere  vesicle."  Wenrich  (1916) 
interprets  these  vesicles  as  expanded  granules. 

In  Collodictyon  the  nuclear  membrane  is  not  one  of  the  most 
evident  features  of  the  resting  nucleus,  but  undoubtedly  it  is  both 
present  and  persistent.  With  the  separation  of  the  microkaryosome 
and  the  beginning  of  organization,  a  second  membrane,  very  faint  but 
evident,  is  formed  immediately  around  the  microkaryosome,  and  pro- 
gressively expands.  Just  around  this  membrane  is  a  progressively 
expanding  hyaline  area,  and '  inside  is  a  more  or  less  homogeneous 
clouded  area  filling  up  the  entire  intramembranous  space,  in  which 
can  also  be  distinguished  the  organizing  microkaryosome,  segmented 
skein  and  spireme.  No  such  membrane  surrounds  the  macrokaryosome 
and  there  is  no  evidence  that  any  kinetic  activity  is  present  in  or 
around  this  mass  of  inert  chromatin. 

R.  S.  Lillie  (1902,  p.  420)  in  discussing  the  oxidative  processes  of 
the  cell-nucleus,  concludes  that  "in  many  tissues  the  nucleus  is  the 
chief  agency  in  the  intracellular  activation  of  oxygen  .  .  .  The  active 
or  atomic  oxygen  is  in  general  most  abundantly  freed  at  the  surface 
of  contact  between  nucleus  and  cytoplasm."  The  nucleus  in  much 
recent  literature  is  regarded  as  the  kinetic  or  metabolic  center  of  cell 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    251 

activity.  It  is  usually  concluded,  on  account  of  this,  that  the  chromatin 
is  the  substance  upon  which  metabolism  is  dependent.  Collodictyon 
presents  evidence  bearing  on  this  point.  The  macrokaryosome,  con- 
sisting of  separated  chromatin,  appears  wholly  passive  during  the 
prophase.  The  microkaryosome,  on  the  other  hand,  consisting  of 
chromatin  which  organizes  the  skein,  is  the  center  of  great  activity.  The 
radius  of  this  activity  is  bounded  by  the  metabolic  membrane.  If  this 
activity  be  regarded  as  due  to  the  entering  into  solution  of  peripheral 
chromatin  and  related  nuclear  substance,  which  must  pass  into  the 
interior,  the  so-called  membrane  must  be  either  merely  a  static  atomic 
equilibrium  zone,  through  which  outer  and  inner  activities  are  counter- 
balanced, or  it  must  be  a  definite  membrane  organized  by  great  pres- 
sure from  within  and  without,  through  which,  by  the  process  of 
osmosis,  the  peripheral  solution  passes  into  the  inner  sphere  of  organ- 
ization, where  the  pressure  is  relieved  and  less  than  on  the  outside,  by 
the  condensation  and  precipitation  of  chromatin  on  the  organizing 
skein.  The  latter  seems  the  more  plausible  interpretation.  In  this 
light  the  generative  chromatin  is  the  kinetic  factor,  at  least  in  mitosis 
probably  in  protozoan  metabolism.  The  free  chromatin  is  non-active 
and  non-kinetic,  acting  in  a  purely  passive  way  in  the  prophase.  Since 
no  food  is  engulfed  and  all  inclusions  are  extruded,  nutritive  pro- 
cesses seem  suspended  in  Collodictyon  during  mitosis.  Oxidative 
(katabolic)  processes  would  naturally  be  at  their  height,  and  better 
subject  to  analysis  since  they  are  here  separate  from  the  anabolic. 
Since  the  chromatin  of  the  macrokaryosome  shows  no  kinetic 
phenomena,  chromatin  as  such  may  be  eliminated  as  the  center  of 
' '  activation  of  oxygen. ' '  But  since  this  oxidative  katabolism  is  a  part 
of  nuclear  activity,  it  is  possible  that  it  may  be  performed  by  the 
generative  chromatin  in  Collodictyon,  possibly  in  other  protozoans; 
while  anabolic  or  constructive  processes  of  intussusception  may  find 
their  center  in  chromatin. 

There  seems  little  doubt  that  the  metabolic  membrane  found  in 
Collodictyon  is  related  in  some  way  to  the  chromosome  vesicles  of  the 
Metazoa,  especially  the  radiations  from  the  karyosome  in  a  proto- 
karyon  type  of  nucleus.  By  its  unity  and  simplicity  I  judge  it  to  be 
more  primitive.  The  chromosome  vesicles  fuse  as  mitosis  progresses 
in  higher  forms;  in  Collodictyon  it  begins  as  a  unit  and  ends  in 
becoming  practically  continuous  with  the  nuclear  membrane.  It 
may  not  be  too  imaginative  to  regard  the  nuclear  membrane  itself, 
with  its  peculiar  phenomena  of  persistence  or  disappearance  in  mitosis. 


252  University  of  California  Publications  in  Zoology        [VOL.  19 

as  related  in  some  way  to  this  kinetic  membrane,  either  in  origin  or  in 
underlying  causes. 

The  substance  of  the  microkaryosome  is  quantitatively  smaller  than 
the  chromatin  of  the  metaphase  chromosomes  (equatorial  plate). 
These  latter  seem  undoubtedly  to  be  derived  from  both  peripheral  and 
karyosome  chromatin.  The  most  probable  way  in  which  peripheral 
chromatin  can  get  upon  the  skein  or  into  the  metabolic  membrane,  is 
by  entering  into  solution  and  being  again  deposited  on  the  inner 
achromatic  framework,  within  the  membrane.  This  would  eliminate 
any  interpretation  of  the  continuity  of  all  of  the  substance  of  chromo- 
somes in  Collodictyon.  Much  has  been  written  of  late  concerning  the 
individuality  of  chromosomes  and  this  is  regarded  by  many  as  funda- 
mental to  any  mechanism  of  Mendelian  inheritance,  especially  as 
interpreted  by  Jannsen  and  Morgan  in  their  ' '  chiasma-type  theory ' '  or 
"theory  of  crossing  over."  Wenrich  (1916)  presents  probably  the 
best  morphological  evidence  of  the  continuity  of  the  chromosomes,  so 
far  recorded.  He,  however,  does  not  claim  to  present  observable  proof 
of  such  continuity,  but  finds  in  his  observations  and  correlations, 
together  with  reasonable  conclusions  from  hybridization  and  other 
experiments,  that  the  evidence  is  greatly  in  favor  of  such  continuity. 
Moenkhaus'  (1904)  conclusion  from  his  hybridization  experiments  is 
typical:  "If  from  such  a  nucleus,  two  kinds  of  chromosomes  again 
emerge,  it  amounts  almost  to  a  demonstration  that  the  chromatin 
substance  of  a  given  chromosome  forms  a  unit  and  that  unit  persists. ' ' 

In  Collodictyon  the  chromatin  cycle  consists  of  an  apparently 
homogeneous  karyosome,  separation  and  possible  elimination  of  major 
part,  an  apparent  solution  phase,  prophase  segmented  spireme  with 
terminal  knobs,  metaphase  chromosomes,  anaphase  synizesis  and 
growth,  followed  by  a  typical  spireme  of  small  nodular  granules, 
which  later  unite  into  irregular  masses,  from  which  the  daughter 
karyosome  is  reorganized. 

INHERITANCE  IN  BINARY  FISSION 

In  sexual  plants  and  animals  the  hereditary  substance  can  be 
localized  in  the  germ  cells,  though  all  reproduction  is  not  by  means 
of  such  germ  plasm.  In  flagellates,  reproducing  alone  by  the  method 
of  simple  binary  fission,  and  in  which  sex  is  unknown,  the  problem  of 
heredity  becomes  more  complex,  instead  of  simpler  of  analysis. 

Were  the  problem  solved  for  higher  organisms,  those  conclusions 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    253 

might  be  extended  to  the  majority  of  the  simpler  Protista,  but  not 
necessarily  to  all.  For  in  this  group  nature  has  her  experimental 
laboratory,  and  we  would  expect  to  find  discards.  "We  may  well 
believe  that  the  mechanism  found  in  sexual  plants  and  animals  is  an 
extremely  modified  and  specialized  adaptation  of  a  much  simpler,  more 
fundamental,  but  thoroughly  satisfactory  type,  characteristic  of  most 
binary  fission  as  found  today.  So  much  at  least  we  may  assume. 

Parthenogenesis  might  be  pointed  to  as  a  reversion  to  such  a  primi- 
tive type  and  such  may  be  the  case ;  but  a  study  of  this  phenomenon 
points  rather  to  its  being  a  still  further  specialization  and  adaptation, 
based  upon  advanced  sexual  phenomena  or  their  suspension.  If  such  be 
the  case,  we  need  not  look  here  for  the  simpler  type  mechanism  of 
inheritance  characteristic  of  binary  fission.  Some  do  regard  it  as 
such,  however,  and  such  an  interpretation  naturally  leads  to  the  con- 
clusion that  sex  is  a  universal  phenomenon.  Minchin  (1912,  p.  130) 
makes  the  generalization  that  sex  is  "of  universal  occurrence  in  all 
truly  cellular  organisms. ' '  This  attitude  does  not  seem  to  accord,  nor 
can  it  be  satisfactorily  harmonized  with  facts  as  understood  today. 
Coulter  (1914)  would  refute  such  a  view,  at  least  in  algae.  In  the 
simpler  flagellates  a  satisfactory  example  of  syngamy  has  yet  to  be 
found.  Dobell's  (1908)  life  cycle  of  Copromonas  has  not  been  veri- 
fied. What  he  figures  as  maturation  phenomena  may  be  well  explained 
by  comparing  his  figures  with  the  differential  division  of  the  karyo- 
some  in  Collodictyon.  Still  variation  and  evolution  are  characteristic 
of  flagellates.  In  fact,  it  is  back  to  the  flagellates  that  the  origin  of 
higher  plants  and  animals  is  traced  by  the  large  majority  of  biologists. 

It  is  little  that  Collodictyon  adds  to  this  much  discussed  subject. 
There  is  a  mitotic  figure,  a  mechanism  which  may  well  be  interpreted 
as  a  distributor  of  hereditary  characters.  Chromosomes  are  present. 
The  actual  number  of  these  in  Collodictyon,  as  in  most  Protozoa,  is 
very  difficult  to  determine.  They  seem  composed  for  the  most  part, 
the  most  evident  part,  of  chromatin,  probably  upon  an  achromatic 
center  or  skeletal  structure.  Such  achromatic  elements  must  not  be 
confused  with  "interzonal  or  connecting  fibers,"  exposed  by  the 
diverging  chromosomes  (pi.  12,  figs.  51-53).  The  chromosomes  in  the 
metaphase  split  transversely.  Such  a  transverse  division  is  capable 
of  interpretation  as  a  longitudinal  split  in  two  ways.  Either  the 
chromosomes  split  longitudinally,  separate  at  one  end  and  finally  pull 
apart  at  the  other  end,  or,  during  the  precocious  splitting  of  the 
spireme  and  final  prophase  the  number  of  chromosomes  is  doubled 


254  University  of  California  Publications  in  Zoology        [VOL.  19 

(pi.  11,  fig.  47),  these  being  fused  end  to  end  into  half  the  number  on 
the  equatorial  plate.  It  is,  then,  these  doubled  chromosomes  which 
separate  transversely  in  the  metaphase.  A  third  alternative  is  that 
the  chromosomes  do  split  transversely,  the  inheritable  characters  being 
usually  halved  physiochemically  but  not  necessarily  according  to  the 
chiasma-type  hypothesis. 

In  behavior,  at  least;  there  are  two  kinds  of  chromatin.  That  of  the 
macrokaryosome  is  largely  passive,  that  of  the  microkaryosome  is  either 
active  or  activated  by  a  close  association  with  the  division  center.  The 
former  may  possibly  be  analogous  to  the  macronucleus  of  ciliates 
and  the  parabasal  body  of  parasitic  flagellates;  the  latter  to  the 
micronucleus  of  ciliates  and  the  typical  nucleus  of  flagellates.  The 
distinction  of  trophochromatin  and  idiochromatin  might  be  applied 
here  as  well  as  in  any  of  the  typical  usually  cited  instances.  The 
chromatin  may  be  all  of  like  character,  its  behavior  being  determined 
in  all  cases  by  associated  elements.  Its  close  association  with  achro- 
matic elements  and  its  inclusion  in  all  chromosomes  is,  therefore, 
essential. 


GENERAL  SUMMARY 

1.  The  first  evidence  of  mitosis  is  an  unequal  constriction  and 
differential  division  of  the  primary  karyosome  of  the  vesicular  nucleus 
into  a  macrokaryosome  and  a  microkaryosome,  the  latter  alone  func- 
tioning directly  in  the  formation  of  the  prophase  skein. 

2.  The  skein  originates  by  the  successive  segmentation  of  the  micro- 
karyosome, resulting  in  two  crescents  and  four  terminal  knobs. 

3.  These  crescents  split  longitudinally,  producing  presumably  eight 
terminal  knobs  which  are  the  elements  at  least  of  chromosomes.    It  is 
possible  that  one  of  the  terminal  knobs  fails  to  split.    In  this  case  the 
number  of  chromosomes  would  be  seven,  which  coincides  with  the  best 
count  so  far  made. 

4.  Coincident  with  the  beginning  of  the  segmenting  skein,  there  is 
organized    around   the   microkaryosome    a  kinetic   membrane    which 
expands  until  it  becomes  apparently  commensurate  with  the  nuclear 
membrane. 

5.  In  the  final  prophase  there  is  a  precocious  splitting  of  the  seg- 
mented skein,  in  which  the  number  of  terminal  chromatin  masses  is 
doubled,  and  all  are  organized  in  an  equatorial  belt.     These  are  prob- 
ably fused  in  telosynapsis. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciHatum  Carter    255 

6.  The  spindle  is  intranuclear.     There  are  seven  or  eight  chromo- 
somes which  part  transversely  at  the  metaphase. 

7.  Growth  of  chromatin  is  very  rapid  in  the  anaphase.     As  the 
chromatin  passes  to  the  poles   of  the  spindle,   a  distinct   granular 
spireme  is  organized. 

8.  Collodictyon  conforms  to  no  category  in  the  classification  of 
mitoses  of  either  Chatton   (1910)   or  Alexeieff   (1913).      Its  nuclear 
membrane  is  persistent  and  its  centrosome  extranuclear.     A  typical 
paradesmose  is  present.     The  chromosomes  are  organized  from  both 
peripheral  chromatin  and  the  karyosome. 

9.  Collodictyon  is  one  of  the  simplest  of  the  Polymastigotes,  both 
in  morphology  and  mitotic  phenomena. 

10.  The  blepharoplast  consists  of  two  basal  granules,  surrounded 
by  a  granular  archoplasm.     In  the  middle   of  the   prophase   these 
granules   separate  and  divide   into   four,   thus   producing   a  double 
blepharoplast  for  each  daughter  cell.    The  flagella  either  split  or  grow 
out  anew.     The  rhizoplasts  split  longitudinally,  being  doubled  about 
the  time  the  basal  granules  separate. 

11.  Division  finally  takes  place  by  a  longitudinal  constriction  along 
the  sulcus. 


ALEXEIEFF,  A. 

1911o.  La  morphologic  et  la  division  de  Bodo  caudatus.    C.-K.  Soc.  Biol.,  Paris, 

70,  130-32,  11  figs,  in  text. 
1911b.  Sur  la   division   nucleaire   et  1  'enkystement   chez   quelques   Amebes   du 

groupe  Limax.     Ibid.,  70,  455-457. 
1912a.  Sur  la  stade  flagelle  dans  1'evolution   des  Amebes  Limax.     I,   Stade 

flagelle  chez  Amoeba  punctata  Dangeard.     Ibid.,  72,  126-128. 
1912&.  Sur    les    characteres   cytologique    et    la    syst&natique    des    amebes    du 

groupe  Limax  (Naegleria  nov.  gen.  et  Hartmannia  nov.  gen.)  et  des 

Amebes    parasites    des    vertebres    (Proctamoeba   nov.    gen.).      Bull. 

Soc.  Zool.  France,  37,  55-74,  7  figs,  in  text. 
1913.     Systematisation  de  la  mitose  dite  "primitive."     Arch.   f.  Prot.,  29, 

344-363,  7  figs,  in  text; 

1916.  Protozoenstudien  II.     Ibid.,  36,  241-302,  pis.  13-21,  5  figs,  in  text. 
BLOCHMANN,  F. 

1895.     Die    microskopische    Thierwelt    des    Siisswassers.      1.    Abt.,    Protozoa. 

(Hamburg,  Grafe),  xv  +  134  pp.,  7  pis.,  10  figs,  in  text. 
BOECK,  W.  C. 

1917.  Mitosis  in  Giardia  microti.     Univ.  Calif.  Publ.  Zool.,  18,  1-26,  pi.  1, 

1  fig.  in  text. 


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BOVERI,  T. 

1901.  Zellenstudien.  IV,  Ueber  die  Natur  der  Centrosomen.  Jena  Zeitsch., 
35,  1-220,  pis.  1-8,  3  figs,  in  text. 

BUTSCHLI,  O. 

1883-1887.  Mastigophora  in  Bronn's  Klassen  u.  Ordnungen  des  Thierreichs. 
(Leipzig,  Winter's  Verlag),  1,  617-1097,  pis.  39-55. 

CALKINS,  G.  N. 

1898.  The  phylogenetic  significance  of  certain  Protozoan  nuclei.     Ann.  N.  Y. 

Acad.  Sci.,  11,  379-400,  pi.  35. 

1899.  Mitosis  in  Noctiluca  miliaris  and  its  bearing  on  the  nuclear  relations 

of  the  Protozoa  and  Metazoa.    Jour.  Morph.,  15,  711-772,  pis.  40-42. 
1903.     The  Protozoan  nucleus.     Arch.  f.  Prot.  2,  213-237,  1  fig.  in  text. 

1909.  Protozoology.     (New  York,  Lea)  ix  +  349  pp.,  4  pis.,  125  figs,  in  text. 

CAROTHERS,  E.  E. 

1917.  The  segregation  and  recombination  of  homologous  chromosomes  as 
found  in  two  genera  of  Aerididae  (Opthoptera).  Jour.  Morph.,  28, 
445-522,  pis.  1-14,  55  figs,  in  text. 

CARTER,  H.  J. 

1865.  On  the  fresh-  and  salt-water  Ehizopoda  of  England  and  India.  Ann. 
and  Mag.  Nat.  Hist.,  (3),  15,  277-293,  pi.  12. 

CHATTON,  E. 

1910.  Essai  sur  la  structure  du  noyau  et  la  mitose  chez  les  amoebiens,  faits 

et  theories.    Arch.  zool.  exp.  et  gen.  (5),  5,  267-337,  13  figs,  in  text. 

DELAGE,  Y.,  AND  HEROUARD,  E. 

1896.  Traite  de  zoologie  concrete.  I,  La  cellule  et  les  protozoaires.  (Paris, 
Eeinwald),  xxx  +  584  pp.,  870  figs,  in  text. 

DOBELL,  C.  C. 

1908.  The  structure  and  life  history  of  Copromonas  subtilis  nov.  spec.    Quar. 

Jour.  Micr.  Sci.,  52,  75-120,  pis.  4-5,  3  figs,  in  text. 

1909.  Chromidia  and  the  binuclearity  hypothesis.    Ibid.,  53,  279-326,  25  figs. 

in  text. 
DOFLEIN,  E. 

1911.  Lehrbuch  der  Protozoenkunde.     (Ed.  3,  Jena,  Fischer),  xii  +  1043  pp., 

951  figs,  in  text. 

FRANCE,  E. 

1899.     A  Collodlctyon  triciliatum  Cart.  Szervezete.     Ueber  den  Organismus 

von  Collodictyon  triciliatum  Cart.     Termiszetrajzi  Fiizetek,  22,  1-26, 

pi.  1,  6  figs,  in  text. 
GLASER,  H. 

1912.  Untersuchungen  iiber  die  Teilung  einiger  Amoben  zugleich  ein  Beitrag 

zur  Phylogenie  des  Centrosoms.    Arch.  f.  Prot.,  25,  27-152,  pis.  3-8, 
5  figs,  in  text. 

GOLDSCHMIDT,   E. 

1907.  Zur  Lebensgeschichte  der  Mastigamoben  Mastigella  vitrea  n.  sp.  und 
Mastigina  setosa  n.  sp.  Ibid.,  Suppl.  1,  83-168,  pis.  5-9. 

GREELEY,  A.  W. 

1903.  The  artificial  production  of  spores  in  Monas  by  a  reduction  of  tem- 
perature. Univ.  Chicago,  Decennial  Publ.,  1,  73-77,  5  figs,  in  text. 


1919]     Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    257 

HARTMANNN,  M. 

1907.  Das  System  der  Protozoen.     Arch.  f.  Prot.,  10,  139-57,  3  figs,  in  text. 
1911.     Die  Konstitution  der  Protistenkerne.     (Jena,  Fischer,  i  +  54  pp.,  13 

figs,  in  text. 

1914.  Bemerkungen  liber  Amoeba  lacertae  Hartmann;  eine  Antwort  am  Clif- 

ford Dobell.     Arch.  f.  Prot.,  34,  336-340,  6  figs,  in  text. 

HARTMANN,  M.,  AND  CHAGAS,  C. 

1910.  Flagellaten-Studien.  Mem.  Inst.  Osw.  Cruz,  2,  64-122,  pis.  4-9,  3  figs. 
in  text. 

HARTMANN,  M.,  AND  JOLLOS,  V. 

1910.  Die  Flagellatenordnung  Binucleata.  Phylogenetisehe  Entwicklung  und 
systematische  Einteilung  der  Blutparasiten.  Arch.  f.  Prot.,  19,  81- 
101,  12  figs,  in  text. 

HERTWIG,  E. 

1902.     Die  Protozoen  und  die  Zelltheorie.     Arch.  f.  Prot.,  1,  1-40. 

KEEBLE,  FREDERICK 

1908.  The  yellow-brown  cells  of  Convoluta  paradoxa,    Quar.  Jour.  Micr.  Sei., 

n.s.,  52,  431-481,  3  plates. 

KENT,  W.  S. 

1880-1882.  A  manual  of  the  Infusoria.  (London,  Bogue),  x  +  472  pp.,  51 
pis. 

KEPNER,  W.  A.,  and  EDWARDS,  J.  G. 

1916.  Nucleus  of  Cliilomonas  paramoecium  Ehrenberg.     Biol.  Bull.,  31,  213- 

219,  6  figs,  in  text. 

KEUTEN,  J. 

1895.  Die  Kerntheilung  von  Euglena  viridis  Ehrenberg.  Zeitschr.  f.  wiss. 
Zool.,  60,  215-235,  pi.  11. 

KLEBS,  G. 

1893.     Flagellatenstudien,  I  u.  II.    Ibid.,  55,  353-445,  pis.  13-16. 

KOFOID,  C.  A. 

1917.  The  biological  and  medical  significance  of  intestinal  flagellates.    Proc. 

2d  Pan-Amer.  Sci.  Cong.,  10,  546-565. 

KOFOID,  C.  A.,  AND  CHRISTIANSEN,  E.  B. 

1915.  Binary  and  multiple  fission  in  Giardia  muris   (Grassi).     Univ.  Calif. 

Publ.  Zool.,  16,  3-54,  pis.  5-8,  1  fig.  in  text. 

KOFOID,  C.  A.,  AND  McCuLLOCH,  IRENE. 

1916.  On  Trypanosoma  triatomae,  a  new  flagellate  from  a  hemipteran  bug 

from  the  nests  of  the  wood  rat  Neotoma  fuscipes.     Univ.  Calif. 
Publ.  Zool.,  16,  113-126,  pis.  14-15. 

KOFOID,  C.  A.,  AND  SWEZY,  OLIVE. 

1915o.  Mitosis  in  Trichomonas.     Proe.  Nat.  Aead.  Sci.,  Wash.,  1,  315-321,  9 

figs,  in  text. 
1915&.  Mitosis  and  multiple  fission  in  trichomonad  flagellates.     Proc.  Amer. 

Acad.  Arts  and  Sci.,  Boston,  51,  289-378,  pis.  1-8,  7  figs,  in  text. 

LANKESTER,  EAY. 

1909.  A  treatise  on  Zoology.     Pt.  I.     (London,  Black),  xxii  +  296  pp.,  151 

figs,  in  text. 


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LEMMERMANN,  E. 

1910.  Kryptogamenflora  der  Mark  Brandenburg.  III.  Algen  I:  Schizophy- 
ceen,  Flagellaten,  Peridineen.  (Leipzig,  Borntraeger),  xi  +  712 
pp.,  816  figs,  in  text. 

LILLIE,  K.  S. 

1902.  On  the  oxidative  processes  of  the  cell-nucleus.  Amer.  Jour.  Physiol., 
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McCuLLOCH,  IRENE. 

1915.  An  outline  of  the  morphology  and  life  history  of  Crithidia  leptocoridis 
sp.  nov.  Univ.  Calif.  Publ.  Zool.,  16,  1-22,  pis.  1-4,  1  fig.  in  text. 

MINCHIN,  E.  A. 

1912.     An  introduction  to  the  study  of  the  Protozoa.     (London,  Arnold),  xi 

+  517  pp.,  194  figs,  in  text. 

1914.  Remarks  on  the  nature  of  the  blepharoplasts  or  basal  granules  of 
flagella.  Arch.  f.  Prot.,  34,  212-216. 

MOENKHAUS,  W.  J. 

1904.  The  development  of  the  hybrids  between  Fundulus  heteroclitus  and 
Menidia  notata  with  especial  reference  to  the  behavior  of  the 
maternal  and  paternal  chromatin.  Amer.  Jour.  Anat.,  3,  29-65, 
pis.  1-4. 

MOROFF,  T.,  and  STIASNY,  G. 

1909.     Bau  und  Entwicklung  von  Acanthometron  pellucidum  J.  M.     Arch.  f. 

Prot.,  16,  209-236,  pis.  13,  14,  54  figs,  in  text. 
NAGLER,  K. 

1909.  Entwicklungsgeschichtliche  Studien  iiber  Amoben.  Ibid.,  15,  1-52, 
pis.  1-6. 

1914.  Ueber  Kernteilung  und  Fortpflanzung  von  Cercobodo  agilis  (Moroff) 

emend.  Lemm.     Ibid.,  34,  133-138,  pi.  6. 

PROWAZEK,  S. 

1903cr.  Flagellatenstudien.    Ibid.,  2,  195-212,  pis.  5,  6. 

1903&.  Die  Kernteilung  des  Entosiphon.     Ibid.,  2,  325-328,  12  figs,  in  text. 

SCHAUDINN,  F. 

1904.     Generation  und  Wirtswechsel  bei  Trypanosoma  und  Spirochaeta.    Arb. 

Kais.  Gesund.,  20,  387-439,  20  figs,  in  text. 
SENN,  G. 

1900.  Flagellata  in  Die  natiirlichen  Pflanzenfamilien  Engler  and  Prantl., 
1,  pp.  93-192,  78  figs,  in  text. 

STEIN,  F.  E.  v. 

1878-1883.  Der  Organismus  der  Infusion  stiere.  (Leipzig,  Englemann),  3, 
1-154,  pis.  1-24. 

SWEZY,   O. 

1915.  Binary  and  multiple  fission  in  Hexamitus.     Univ.   Calif.  Publ.  Zool., 

16,  71-88,  pis.  9-11. 

1916.  The  kinetonucleus  of  flagellates  and  the  binuclear  theory  of  Hart- 

mann.     Ibid.,  16,  185-240,  58  figs,  in  text. 

TSCHENZOFF,   B. 

1916.  Die  Kernteilung  bei  Euglena  viridis  Ehrbg.  Arch.  f.  Prot.,  36,  137-173, 
pis.  11-12,  2  figs,  in  text. 


Rhodes:  Binary  Fission  in  Collodictyon  triciliatum  Carter    259 

TURNER,  C.  C. 

1917.     A  culture  medium  for  Euglena.     Science,  45,  239. 

W  ENRICH,  D.  H. 

1916.  The  spermatogenesis  of  Phrynotettiz  magnus  with  special  reference  to 
synapsis  and  the  individuality  of  the  chromosomes.  Bull.  Mus. 
Comp.  Zool.  Harvard  Coll.,  60,  55-133,  pis.  1-10. 

WENYON,  C.  M. 

1910.  Observations  on  a  flagellate  of  the  genus  Cercomonas.  Quar.  Jour. 
Micr.  Sci.,  55,  241-260,  19  figs,  in  text. 

WERBITISKI,  F.  W. 

1910.  TJeber  blepharoplastlose  Trypanosomen.  Centrl.  Bakt.  5  (53),  3,  303- 
315,  pis.  1-2,  2  figs,  in  text. 

WILSON,  C.  W. 

1915.  On  the  life-history  of  a  soil  amoeba.  Univ.  Calif.  Publ.  Zool.,  16, 
241-292,  pis.  18-23. 


EXPLANATION  OF  PLATES 

Figures  in  plates  7  and  14  are  diagrammatic,  those  of  plate  7  being  based 
upon  observations  of  living  and  stained  material,  plate  14  being  sketched  from 
camera  lucida  drawings  of  accompanying  plates.  Figures  in  plates  8  to  13  are 
camera  lucida  sketches.  All  figures  except  plate  13,  figure  62,  are  of  Collodictyon 
triciliatum  Carter,  killed  in  hot  Schaudinn  's  fluid  and  stained  in  Heidenhain  's 
aqueous  iron-alum  haematoxylin,  unless  otherwise  stated.  X  1700. 

PLATE  7 

Fig.  1.  Laterosulcal  view,  showing  vacuolated  cytoplasm,  sulcus,  vesicular 
nucleus  with  karyosome  and  peripheral  chromatin,  blepharoplast  of  two  basal 
granules  surrounded  by  granular  archoplasm,  four  flagella,  and  rhizoplast. 

Fig.  2.  Absulcal  view,  showing  bifurcated  posterior  end,  nucleus,  blepharo- 
plast, and  flagelia. 

Fig.  3.  Sulcal  view,  showing  median  sulcus,  posterior  bifurcation,  nucleus, 
blepharoplast  and  flagella. 

Fig.  4.  Anterior  view,  showing  sulcus,  nucleus,  blepharoplast,  rhizoplast, 
and  four  flagella. 

Fig.  5.     Sulcal  view  of  truncated  posterior  end;  two  cusps. 

Fig.  6.     Sulcal  view  of  truncated  posterior  end;  three  cusps. 

Fig.  7.     Laterosulcal  view  of  truncated  posterior  end;  four  cusps. 

Fig.  8.     Laterosulcal  view  of  truncated  posterior  end;  five  cusps. 


[260] 


[RHODES]   PLATE  .7 


PLATE  8 
Figures  9  to  18,  showing  variations  in  size  and  shape. 

Figs.  9  and  16,  from  material  killed  in  picro-mercuric,  stained  in  Bordeaux  R, 
aqueous  iron  haematoxylin. 

Figs.  10,  13,  and  18,  from  material  killed  in  strong  Flemming,  stained  in 
aqueous  iron-alum  haematoxylin. 

Figs.  11,  14,  and  15,  from  material  killed  in  hot  Schaudinn  's  fluid,  stained  in 
alcoholic  iron-alum  haematoxylin. 

Fig.  12,  from  material  killed  in  picro-mercuric,  stained  in  Mallory's  connec- 
tive tissue  stain,  modified. 

Fig.  17,  from  material  killed  in  picro-mercuric  stained  in  phosphotungstic 
acid  haematoxylin. 


[262] 


UNIV.  CALIF.  PUBL.  ZOOL.  VOL.  19 


[RHODES]   PLATE   8 


^, 

,.C^s  , 


18 


PLATE  9 

Figures  19  to  27,  showing  food  inclusions,  fig.  19  killed  in  hot  Schaudinn's 
fluid,  fig.  26  killed  in  strong  Flemming's  and  stained  in  iron  haematoxylin,  and 
figs.  20-25  and  27  killed  in  strong  Flemming's  and  stained  in  Bordeau  E  iron 
haematoxylin. 

Fig.  19.     Ulothrix. 

Fig.  20.     Two  dinoflagellates,  presumably  Peridinium. 

Fig.  21.     Gelatinous  capsule  of  Pandorina  and  Scenedesmus. 

Fig.  22.     Scenedusmus. 

Fig.  23.     Pediastrum. 

Fig.  24.     A  diatom,  presumably  Navicula. 

Fig.  25.     A  ciliate,  presumably  Colpidium. 

Fig.  26.     A  diatom,  presumably  Navicula. 

Fig.  27.     Pandorina. 


[264] 


UNIV.  CALIF.  PUBL.  ZOOL.  VOL    19 


[RHODES]   PLATE  9 


.  * 


25 


26 


27 


PLATE  10 

Prophase. 

Fig.  28.  Typical  vesicular  nucleus.  Chromidial  granules  forming  around  the 
hyaline  area. 

Fig.  29.     Unequal  constriction  of  primary  karyosome. 

Fig.  30.  Unequal  constriction  of  primary  karyosome.  Organization  of 
peripheral  chromatin  into  granules  connected  by  a  slightly  chromatic  con- 
tinuous fiber.  Partial  separation  of  basal  granules. 

Fig.  31.  Differential  division  of  primary  karyosome  into  a  macrokaryosome 
and  a  microkaryosome.  Kinetic  membrane  surrounding  the  microkaryosome. 

Fig.  32.  The  same  as  figure  31  with  peripheral  chromatin  encrusted  upon 
the  nuclear  membrane.  Extranuclear  chromidial  cloud. 

Fig.  33.  The  unequal  constriction  of  the  macrokaryosome.  Note  the  granular 
organization  of  the  microkaryosome. 

Fig.  34.     First  signs  of  segmentation  of  microkaryosome. 

Fig.  35.  Segmenting  microkaryosome  with  fibers  connecting  the  two  polar 
chromidial  masses.  Intranuclear  chromidial  cloud. 

Fig.  36.  The  same  as  figure  35;  nucleus  elongated;  peripheral  chromatin 
granules;  separation  of  basal  granules,  only  four  flagella. 


[266] 


UNIV.  CALIF.  PUBL.  ZOOL.  VOL.  19 


32 


36 


PLATE  11 
Prophase. 

Fig.  37.  Chromidial  masses  with  connecting  fibers  in  the  segmenting  skein. 
Chromidial  cloud  within  the  kinetic  membrane.  Macrokaryosome  being  pushed 
aside  by  the  expanding  kinetic  membrane.  Peripheral  chromatin  gathered  just 
within  the  nuclear  membrane. 

Fig.  38.  Macrokaryosome  in  a  niche  of  the  nuclear  membrane.  The  seg- 
menting skein  within  a  precocious  spindle  formation. 

Fig.  39.     Further  organization  of  the  skein  into  the  tripod  stage. 

Fig.  40.  Tripod  stage  of  segmenting  spireme.  Peripheral  chromatin  in 
larger  granules.  Further  separation  and  initial  division  of  basal  granules,  pro- 
ducing four  basal  granules  and  eight  flagella,  splitting  of  rhizoplast. 

Fig.  40a.  Another  view  of  figure  40,  showing  the  four  basal  granules. 

Fig.  41.  Segmenting  skein  in  the  form  of  a  double  crescent  with  four 
terminal  knobs  of  chromatin.  Two  small  granules  which  may  be  the  division 
center.  Chromidial  cloud  within  the  kinetic  membrane,  macrokaryosome  passive. 

Fig.  42.     Same  as  figure  41. 

Fig.  43.     Disintegration  of  macrokaryosome.    A  moribund  stage. 

Fig.  44.  Expanding  kinetic  membrane  commensurate  with  the  nuclear  mem- 
brane. Macrokaryosome  in  a  niche  of  the  nuclear  membrane.  Some  chromatin 
still  encrusted,  upon  the  membrane.  Khizoplast  evident. 

Fig.  45.  Longitudinal  splitting  of  segmenting  skein,  producing  seven  or 
eight  terminal  knobs,  in  all  probability  the  elements  of  the  future  chromosomes. 

Fig.  46.  Blepharoplasts  separated.  Precocious  splitting  of  peripheral 
chromatin.  A  precocious  equatorial  plate  with  macrokaryosome  apparently 
upon  it. 


[268] 


[RHODES]   PLATE    11 


44 


PLATE  12 
Metaphase,  Anaphase  and  Telophase. 

Fig.  47.  Precocious  splitting  of  the  terminal  knobs  of  the  final  segmenta- 
tion skein,  forming  an  equatorial  belt  of  chromidial  cloud  in  which  are  embedded 
eight  paired  chromatin  masses.  Final  prophase. 

Fig.  48.  Metaphase  equatorial  plate.  Macrokaryosome  apparently  a  part 
of  it.  Two  blepharoplasts  of  two  basal  granules  each.  Spindle  oriented  either 
in  relation  to  the  blepharoplasts  or  the  major  axis  of  the  cell.  Intranuclear 
chromidial  cloud. 

Fig.  49.  Same  as  figure  48;  chromatin  granules  lodged  upon  the  spindle 
fibers.  Clearing  up  of  intranuclear  chromidial  cloud. 

Fig.  50.  Metaphase  spindle.  Seven  chromosomes  can  be  seen,  one  being 
only  half  so  large  as  the  others.  Transverse  splitting  of  all  chromosomes  except 
the  small  one.  No  chromatin  within  the  nucleus  except  that  upon  the  equatorial 
plate.  No  evidence  of  maerokaryosome,  peripheral  chromatin,  or  centrosome 
granules.  From  material  killed  in  hot  Schaudinn  's  fluid  and  stained  in  saf ranin, 
gentian-violet,  orange  G. 

Fig.  51.  Anaphase.  Unequal  amounts  of  chromatin  passing  to  the  daughter 
poles.  The  chromosomes  are  stuck  together.  Intranuclear  chromidial  cloud. 

Fig.  51.  Anaphase.  Irregularly  lobed  chromatin  masses  collected  at  respec- 
tive daughter  poles.  Separation  fibers  evident.  Intranuclear  chromidial  cloud. 

Fig.  53.  Anaphase.  Organization  of  daughter  chromatin  masses  into  linear 
skeins.  Daughter  rhizoplasts  connecting  the  daughter  blepharoplasts. 

Fig.  54.  Telophase.  Daughter  nuclei  separated.  Intra-  and  extranuclear 
chromidial  cloud.  Daughter  blepharoplasts  and  related  nuclei  shifted  to  opposite 
sides  of  the  sulcus. 

Fig.  55.  Telophase.  Same  as  figure  54.  Extranuclear  chromidial  cloud 
deepens. 

Fig.  56.  Chromatin  has  separated  out  into  four  large  masses,  an  extra  large 
mass  being  in  one  daughter  cell.  Daughter  rhizoplasts  heavy. 


[270] 


UN IV.  CALIF.  PUBL.  ZOOL.  VOL.  19 


[RHODES]   PLATE    12 


52 


56 


PLATE  13 

Fig.  57.  Telophase.  Cytoplasmic  constriction  along  the  sulcus.  Blepharo- 
plasts  deeply  stained.  Rhizoplasts  evident.  Heavy  extranuclear  chromidial 
cloud.  Chromatin  further  broken  up  into  irregular  masses. 

Fig.  58.  Large  vacuole  in  the  cytoplasmic  connective.  Further  dissociation 
of  chromatin  masses  into  granules  which  show  the  beginning  of  concentric 
organization. 

Fig.  59.  Reorganization  of  central  karyosome  and  peripheral  chromatin. 
From  material  killed  in  Flemming  strong,  and  stained  in  Bordeaux  E  iron 
haematoxylin. 

Fig.  60.  Suspended  telophase.  Engulfed  Pandorina  in  food  vacuole.  Karyo- 
some and  peripheral  chromatin.  Small  chromatin  mass  outside  the  karyosome 
of  unknown  significance,  possibly  the  division  center.  From  material  killed  in 
Flemming  strong,  and  stained  in  Bordeaux  E  iron  haematoxylin. 

Fig.  61.  Individual  just  after  fission  is  completed.  Double  rhizoplast  ex- 
tending into  karyosome.  Chromidial  organization  still  evident  in  the  karyosome. 

Fig.  62.  Somatella,  probably  of  sixteen  cells,  of  Amoeba  radiosa.  At  first 
considered  a  Collodictyon  cyst.  Such  may  possibly  be  the  case  though  reaction 
to  the  stain  does  not  warrant  such  a  conclusion.  X  1900. 


\272] 


UNIV.  CALTF.  PUBL.  ZOOL.  VOL.  19 


[RHODES]   PLATE   13 


* V;*.    •  '••l:»- .     .-1 


62 


PLATE  14 

Nuclear  changes  in  binary  fission  in  Collodictyon.  Any  differences  between 
these  figures  and  those  of  associated  plates  must  be  referred  to  the  original 
camera  lucida  sketches  for  critical  interpretation. 

Figs.  65-76.     Prophase  phenomena. 

Figs.  63-65.     Stages  of  the  resting  nucleus. 

Figs.  77-79.     Metaphase. 

Figs.  80-83.     Anaphase. 

Figs.  84-87.     Telophase. 

Figs.  66-67.     Unequal  constriction  of  primary  karyosome. 

Fig.  68-69.  Differential  division  of  the  primary  karyosome  into  a  macro- 
karyosome  and  a  microkaryosome.  Organization  of  a  kinetic  membrane  around 
the  microkaryosome. 

Figs.  69-73.  The  segmenting  skein,  with  associated  expansion  of  the  kinetic 
membrane. 

Fig.  71.  Precocious  spindle  formation.  Macrokaryosome  in  a  niche  of  the 
nuclear  membrane. 

Fig.  72.  Double  crescent  stage  of  segmenting  skein  showing  four  terminal 
knobs  and  a  possible  intranuclear  division  center  dividing. 

Fig.  73.  Longitudinal  splitting  of  crescents,  producing  seven  or  eight  termi- 
nal knobs  of  chromatin  which  are  the  elements  of  the  chromosomes. 

Fig.  74.  Precocious  spliting  of  peripheral  chromatin  granules.  Precocious 
equatorial  plate  formation  with  macrokaryosome  upon  it. 

Fig.  75.  Final  prophase.  Division  of  blepharoplasts  with  apparent  splitting 
of  flagella;  separating  centrosomes  upon  the  nuclear  membrane  connected  by  a 
paradesmose. 

Fig.  76.  Precocious  splitting  of  final  stage  of  segmenting  skein.  Sixteen 
chromatin  masses  in  a  chromatin  cloud  in  the  form  of  an  equatorial  belt. 

Fig.  77.  Metaphase  spindle.  Macrokaryosome  apparently  a  part  of  it. 
Intranuclear  chromatin  cloud. 

Fig.  78.  Metaphase  spindle;  centrosomes  at  poles  of  spindle  and  connected 
by  paradesmose. 

Fig.  79.  Metaphase  spindle  showing  seven  chromosomes.  Transverse  parting 
of  all  chromosomes  except  one  which  is  only  half  so  large  as  the  rest. 

Fig.  80.     Anaphase.     Apparent  unequal  distribution  of  chromatin. 

Fig.  81.  Anaphase.  Daughter  chromatin  masses  organized  into  linear 
spiremes. 

Fig.  82.  Anaphase.  Linear  spireme  of  chromatin  granules  closely  related 
to  centrosomes,  which  are  connected  by  paradesmose. 

Fig.  83.  Telophase.  Complete  separation  of  daughter  nuclei.  Extranuclear 
and  intranuclear  chromidial  cloud. 

Fig.  85.     Distribution  of  chromatin  as  granules  throughout  nucleus. 

Fig.  86.  Eeorganization  of  central  karyosome  with  surrounding  hyaline  area, 
and  peripheral  chromatin. 

Fig.  87.  Suspended  telophase.  Vesicular  nucleus  with  small  chromatin  mass 
of  unknown  significance  near  the  periphery.  Daughter  blepharoplasts  with 
double  basal  granules  surrounded  by  granular  archoplasm. 


[274] 


UNIV.  CALIF.  PUBL.  ZOOL.  VOL.  19 


[RHODES]   PLATE   14 


65 


71 


78 


79 


- 


• 

•  :  :':-.•  •/ 


;t  * 


81 


83 


69 


70 


74 


77 


78 


84 


s 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

7.  The  Subspecies  of  Seeloporus  occidentals,  with  Description  of  a  New  Form 

from  the  Sierra  Nevada  and  Systematic  Notes   on  Other   California 
Lizards,  by  Charles  Lewis  Camp.    Pp.  63-74.    December,  1916 JLO 

8.  Osteological  Relationships  of  Three  Species  of  Beavers,  by  F.  Harvey 

Holden.    Pp.  75-114,  plates  5-12,  18  text  figures.    March,  1917 .40 

9.  Notes  on  the  Systematic  Status  of  the  Toads  and  Frogs  of  California,  by 

Charles  Lewis  Camp.    Pp.  115-125,  3  text  figures.    February,  1917 .10 

10.  A  Distributional  List  of  the  Amphibians  and  Reptiles  of  California,  by 

Joseph  Grinnell  and  Charles  Lewis  Camp.    Pp.  127-208,  14  figures  in  text. 
July,  1917  .85 

11.  A  Study  of  the  Races  of  the  White-Fronted  Goose  (Anser  alMfrons}  occur- 

ring in  California,  by  H.  S.  Swarth  and  Harold  0.  Bryant.    Pp.  209-222, 

2  figures  in  text,  plate  IS.    October,  1917 _ .15 

12.  A  Synopsis  of  the  Bats  of  California,  by  Hilda  Wood  Grlnneli.    Pp.  223-404, 

plates  14-24,  24  text  figures.    January  31,  1918  2.00 

13.  The  Pacific  Coast  Jays  of  the  Genus  Aphelocoma,  by  H.  S.  Swarth.    Pp. 

405-422,  1  figure  in  text.    February  23,  1918 .20 

14.  Six  New  Mammals  from  the  Mohave  Desert  and  Inyo  Regions  of  California, 

by  Joseph  Grinnell.    Pp.  423-430. 

15.  Notes  on  Some  Bats  from  Alaska  and  British  Columbia,  by  Hilda  Wood 

Grinnell.    Pp.  431-433. 

Nos.  14  and  15  in  one  cover.    April,  1918 „      .16 

16.  Revision  of  the  Rodent  Genus  Aplodontia,  by  Walter  P.  Taylor.    Pp.  435- 

504,  plates  25-29,  16  text  figures.    May,  1918 75 

17.  The  Subspecies  of  the  Mountain  Chickadee,  by  Joseph  Grinnell.    Pp.  SOS- 

SIS,  3  text  figures.    May,  1918  _ 15 

18.  Excavations  of  Burrows  of  the  Rodent  Aplodontia,  with  Observations  on 

the  Habits  of  the  Animal,  by  Charles  Lewis  Camp.    Pp.  517-536,  6  figures 

in  text.    June,  1918  _      .20 

Index,  pp.  537-545. 

L  18.   1.  Mitosis  in  Giardia  microti,  by  William  C.  Boeck.     Pp.  1-26,  plate  1.    Octo- 
ber, 1917  .35 

f.  An  Unusual  Extension  of  the  Distribution  of  the  Shipworm  in  San  Fran- 
cisco Bay,  California,  by  Albert  L.  Barrows.  Pp.  27-43.  December,  1917.  .20 

3.  Description  of  Some  New  Species  of  Polynoidae  from  the  Coast  of  Cali- 

fornia, by  Christine  Essenberg.    Pp.  45-60,  plates  23.    October,  1917 .20 

4.  New  Species  of  Amphinomidag  from  the  Pacific  Coast,  by  Christine  Essen- 

berg.    Pp.  61-74,  plates  4-5.    October,  1917  .16 

6.  Crithidia  curyopMhalmi,  sp.  nov.,  from  the  Hemipteran  Bug,  Euryophthalmu* 
convivus  Stal,  by  Irene  McCulloch.  Pp.  75-88,  35  text  figures.  Decem- 
ber, 1917  JL5 

6.  On  the  Orientation  of  Erythropxis,  by  Charles  Atwood  Kofoid  and  Olive 

Swezy.  Pp.  89-102,  12  figures  in  text.    December,  1917 .15 

7.  The  Transmission  of  Nervous  Impulses  in  Relation  to  Locomotion  in  the 

Earthworm,  by  John  F.  Bovard.    Pp.  103-134, 14  figures  in  text.   January, 
1918    .35 

8.  The  Function  of  the  Giant  Fibers  in  Earthworms,  by  John  F.  Bovard.    Pp. 

135-144,  1  figure  in  text.    January,  1918  _„ _ .10 

9.  A  Rapid  Method  for  the  Detection  of  Protozoan  Cysts  In  Mammalian 

Faeces,  by  William  C.  Boeck.    Pp.  145-149.    December,  1917 _      .05 

10.  The  Musculature  of  Heptanchut  maoulatus,  by  Pirie  Davidsou...  Pp.  151-170, 

12  figures  in  text.    March,  1918 _ _ 25 

11.  The  Factors  controlling  the  Distribution  of  the  Polynoidae  of  the  Pacific 

Coast  of  North  America,  by  Christine  Essenberg.    Pp.  171-238,  plates  6-8, 

2  figures  in  text.    March,  1918-  - _ _ .75 

12.  Differentials  In  Behavior  of  the  Two  Generations  of  Salpa  democratica 

Relative  to  the  Temperature  of  the  Sea,  by  "RUte  L.  Michael.    Pp.  239-298, 
plates  9-11, 1  figure  in  text.    March,  1918 „ .65 

13.  A  Quantitative  Analysis  of  the  Molluscan  Fauna  of  San  Francisco  Bay,  by 

E.  L.  Packard.    Pp.  299-336,  plates  12-13,  6  figs.  In  text.    April,  1918 .40 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

14.  The  Neuromotor  Apparatus  of  Euplotes  patella,  by  Harry  B.  Yocom.    Pp. 

337-396,  plates  14-16.    September,  1918  .70 

15.  The  Significance  of  Skeletal  Variations  in  the  Genus  Peridinium,  by  A.  L. 

Barrows.    Pp.  397-478,  plates  17-20,  19  figures  in  text.    June,  1918 .90 

16.  The  Subclavian  Vein  and  its  Eolations  in  Elasmobranch  Fishes,  by  J. 

Frank  Daniel.    Pp.  479-484,  2  figures  in  text.    August,  1918 JLO 

17.  The  Cercaria  of  the  Japanese  Blood  Fluke,   Schistosoma  japonicum  Kat- 

surada,  by  William  W.  Cort,    Pp.  485-507,  3  figures  in  text. 

18.  Notes  on  the  Eggs  and  Miracidia  of  the  Human  Schistosomes,  by  William 

W.  Cort.    Pp.  609-519,  7  figures  in  text. 

Nos.  17  and  18  in  one  cover.    January,  1919 .35 

Index  in  preparation. 

Vol.19.  1.  Reaction  of  Various  Plankton  Animals  with  Reference  to  their  Diurnal 

Migrations,  by  Calvin  O.  Esterly.  Pp.  1-83.  April,  1919 85 

2.  The  Pteropod  Desmopterus  pacificus  (sp.  nov.),  by  Christine  Essenberg. 

Pp.  85-88,  2  figures  in  text.  May,  1919  05 

8.  Studies  on  Giardia  microti,  by  William  C.  Boeck.  Pp.  85-136,  plate  1,  19 

figures  in  text  „ .60 

4.  A  Comparison  of  the  Life  Cycle  of  Crithidia  with  that  of  Trypanosoma  in 

the  Invertebrate  Host,  by  Irene  McCulloch.  Pp.  135-190,  plates  2-6,  3 
figures  in  text.  October,  1919  „ 60 

5.  A  Muscid  Larva  of  the  San  Francisco  Bay  Region  which  sucks  the  Blood 

of  Nestling  Birds,  by  O.  E.  Plath.  Pp.  191-200.    February,  1919 J.O 

6.  Binary  Fission  in  Collodictyon  triciliatum  Carter,  by  Robert  Clinton  Rhodes. 

Pp.  201-274,  plates  7-14,  4  figures  in  text.     December,  1919 1.00 

7.  The  Excretory  System  of  a  Stylet  Cercaria,  by  William  W.  Cort.    Pp.  275- 

281,  1  figure  in  text.    August,  1919 10 

8.  A  New  Distome  From  Rana  Aurora,  by  William  W.  Cort.    Pp.  283-298, 

5  figures  in  text.     November,  1919 ~ 20 

Vol.  20.  1.  Studies  on  the  Parasites  of  the  Termites.  I.  On  Streblomastix  strix,  a 
'  ..lymastigote  Flagellate  with  a  Linear  Plasmodial  Phase,  by  Charles 
Atwood  Kofoid  and  Olive  Swezy.  Pp.  1-20,  plates  1-2,  1  figure  in 
text.  July,  1919 25 

2.  Studies  on  the  Parasites  of  the  Termites.    II.    On  Trichomitus  termitidis, 

a  Polymastigote  Flagellate  with  a  Highly  Developed  Neuromotor  System, 
by  Charles  Atwood  Kofoid  and  Olive  Swezy.  Pp.  21-40,  plates  3-4,  2 
figures  in  text.  July,  1919  -. 25 

3.  Studies  on  the  Parasites  of  the  Termites.  III.  On  TrichonympJia  campanula 

Sp.  Nov.,  by  Charles  Atwood  Kofoid  and  Olive  Swezy.  Pp.  41-98,  plates 
5-12,  4  figures  in  text.  July,  1919 75 

4.  Studies  on  the  Parasites  of  the  Termites.     IV.     On  Leidyopsis  sphaerica 
Gen.  Nov.,  Sp.  Nov.,  by  Charles  Atwood  Kofoid  and  Olive  Swezy.    Pp. 
99-116,  plates  13-14,  1  figure  in  text.    July,  1919 „ 25 

Vol.21.  1.  A  Revision  of  the  Microtus  calif ornicus  Group  of  Meadow  Mice,  by  Rem- 
ington Kellogg.  Pp.  1-42,  1  figure  in  text.  December,  1918 _  .50 

2.  Five  New  Five-toed  Kangaroo  Rats  from  California,  by  Joseph  Grinnell 

Pp.  43-47.    March,  1919  05 


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